Composite cured red mud material for salt freezing coupling environment and preparation method of composite cured red mud material

Abstract

The invention relates to the technical field of building materials, and discloses a composite cured red mud material for a salt freezing coupling environment and a preparation method thereof, and the composite cured red mud material comprises 27-49 parts of red mud, 24-47 parts of steel slag, 8-19 parts of fly ash and 3-15 parts of phosphogypsum. The method comprises the following steps: taking red mud, steel slag, fly ash and ardealite as raw materials, putting the raw materials into a stirrer, and fully mixing; adding water, continuously stirring and uniformly mixing to obtain a mixture; pouring the mixture into a mold and pressing into a cylindrical test piece; demolding and weighing, and after the weight is high, sealing and curing to prepare a sample; and soaking the cured sample in a salt solution to simulate a salt-freezing coupling environment, and then taking out the sample for freezing and thawing treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, particularly to the field of red mud-based cementitious materials, and specifically relates to a composite solidified red mud material for salt-freezing coupling environment and a preparation method thereof. Background Art

[0002] Under the background of the accelerating urbanization process and the expanding scale of industrialization, the demand for cement as the main building material is increasing continuously. However, its production process is energy-consuming and highly polluting, imposing a huge burden on the environment. As a feasible alternative, solid waste-based cementitious materials can not only reduce the demand for cement but also reduce environmental pollution through the resource utilization of waste.

[0003] Red mud is an extremely fine particle product generated during the production of alumina by the Bayer process using bauxite as raw material. The quantity of red mud produced in China each year is increasing rapidly, and the stockpile has reached 2 billion tons. Red mud is strongly alkaline and contains a large amount of heavy metals. The piled-up red mud not only occupies a large area of land but also pollutes the surrounding soil and groundwater through particle migration, bringing inconvenience to people's production and life. Currently, the main method for treating accumulated red mud is the microbial method. In addition, there are also some methods for comprehensively utilizing red mud, such as producing materials, recovering rare earth elements, and improving soft soil, etc. However, due to technological limitations, these methods and processes have not been widely applied in production. The harm of the mountainous accumulated red mud to the environment still exists and shows a gradually increasing trend. Using stabilized red mud to replace traditional gravel and cement foundation cushions and using it as a building base filler to achieve effective resource utilization is of great significance.

[0004] In the prior art, many studies have been conducted on using red mud as a foundation filler. However, the existing research on red mud-based materials mainly focuses on the mechanical properties at normal temperature, but there is insufficient research on the durability under the coupled action of salt corrosion and freeze-thaw cycles.

[0005] Problems such as surface spalling and a sharp increase in porosity occur in red mud-based materials after freeze-thaw cycles, resulting in a significant decrease in strength and limiting their application in extreme environments. To solve the above problems, the present invention proposes a composite solidified red mud material for salt-freezing coupling environment and a preparation method thereof. Summary of the Invention

[0006] In order to solve a series of problems in the prior art, such as the accumulation of red mud stockpiles, occupying land and causing pollution, using red mud to replace traditional gravel and cement foundation cushions and using it as a building base filler has been studied, but the existing red mud-based materials cannot meet the environment of the coupled action of salt corrosion and freeze-thaw cycles, and problems such as surface spalling and a sharp increase in porosity will occur, resulting in a significant decrease in strength and limiting their application in extreme environments, the present invention provides a composite solidified red mud material for salt-freezing coupling environment and a preparation method thereof.

[0007] The present invention is implemented by the following technologies: A composite solidified red mud material for a salt-freeze coupled environment comprises 27 to 49 parts of red mud, wherein the pH value of the red mud ranges from 11.4 to 12.2, providing alkaline excitation; 24 to 47 parts of steel slag, supplementing silicon and aluminum active components; 8 to 19 parts of fly ash, enhancing volcanic ash effect; and 3 to 15 parts of phosphogypsum as a sulfate activator.

[0008] Further, it includes 27 to 31 parts of red mud, 41 to 47 parts of steel slag, 17 to 19 parts of fly ash, and 3 to 15 parts of phosphogypsum.

[0009] Furthermore, it also includes 2 to 5 parts of chitosan, 3 to 5 parts of ultrafine quartz powder, and 3 to 5 parts of attapulgite, which are used to solidify heavy metals and inhibit salt corrosion.

[0010] During implementation, a composite solidified red mud material for a salt-freeze coupled environment includes 48.2 parts of red mud, 24.1 parts of steel slag, 8 parts of fly ash, 8.9 parts of phosphogypsum, 2.8 parts of chitosan, 4.1 parts of ultrafine quartz powder, and 3.9 parts of attapulgite.

[0011] The present invention provides a method for preparing a composite solidified red mud material for a salt-freeze coupled environment, comprising the following steps: a. Raw material pretreatment Take red mud, steel slag, fly ash and phosphogypsum as raw materials, put the raw materials into a mixer and mix them thoroughly, preferably, add chitosan, ultrafine quartz powder and attapulgite as raw materials; among the raw materials, the high alkalinity of red mud is used as an alkaline activator to promote the hydration reaction; and phosphogypsum is used as a sulfate activator to react with the calcium components therein to promote the hydration process, and the silicates and aluminates in the steel slag and fly ash participate in the reaction under the action of dual excitation to form a stable calcium silicate aluminum hydration product to prepare a red mud-based quaternary cementitious material. Add water according to a water-cement ratio of 0.3, continue to stir and mix evenly, and obtain a mixture.

[0012] b. Static pressure forming The mixture was poured into a cylindrical sample mold with a specification of Φ50 mm×H50 mm, and was pressed into a cylindrical specimen by a jack static pressure method with a compaction degree of ≥96%.

[0013] c. Maintenance After demoulding, weighing and measuring, place it in a plastic bag, seal it, and place it in an environment with a temperature of 20±2℃ and a humidity of ≥95% for curing to ensure uniform humidity inside the sample and avoid rapid evaporation of water to obtain the test sample.

[0014] d. Salt-freeze coupled environment treatment The freeze-thaw environment simulation is similar to the environmental pressures that may be encountered in natural climatic conditions and actual applications. Extreme seasonal temperature fluctuations and the presence of soluble salts in the soil provide a rigorous test environment for evaluating durability and resistance.

[0015] After 28 days of curing, the specimens are immersed in the salt solution for 24 hours. Based on the highest content of underground corrosion ions, a coupling salt solution with a concentration 10 times higher is prepared to conduct the durability test on the solidified red mud. The salt solution includes 0.02 - 0.05 mol / L of Na2SO4, 0.03 - 0.06 mol / L of Na2CO3, and 0.04 - 0.07 mol / L of NaCl. Specifically, it includes 0.03 mol / L of Na2SO4, 0.04 mol / L of Na2CO3, and 0.05 mol / L of NaCl to simulate the salt-freezing coupling environment. The liquid level is higher than the top surface of the specimen, and it is immersed for 4 days. The salt solution simulates the composite corrosion salt solution environment of the actual service environment. Then, the specimens are taken out for freeze-thaw treatment. The specimens are placed in an environmental chamber with a temperature set at -25°C to -15°C and frozen for 8 - 14 hours, and then taken out and melted at room temperature of 15 - 30°C for 8 - 14 hours, which is regarded as 1 freeze-thaw cycle. The freeze-thaw cycle is carried out 2 - 10 times. Specifically, the specimens are placed in an environmental chamber with a temperature set at -23°C and frozen for 12 hours, and then taken out and melted at room temperature of 25°C for 12 hours. This is 1 freeze-thaw cycle. A complete freeze-thaw cycle is 24 hours, and the freeze-thaw cycle is carried out 2 - 10 times. The number of freeze-thaw cycles for each specimen group is selected as 2, 4, 6, 8, and 10 times respectively.

[0016] Compared with the prior art, the present invention has the following beneficial effects: A composite solidified red mud material for salt-freezing coupling environment and its preparation method provided by this application. The prepared material shows excellent durability after being tested in the simulated composite salt-freezing environment.

[0017] 1) Compared with the traditional cement production process, the environmental impact is reduced by 12%, and the resource recycling is significantly improved. It performs better than traditional cement in various types of environmental impacts, providing an innovative solution for the large-scale disposal of industrial solid waste.

[0018] 2) It has excellent compressive strength. This application not only improves the early strength of the material but also affects the entire hydration process. In the hydration reaction, the calcium aluminosulfate (AFm) phase generated further promotes the hydration reaction of aluminum and silicon. Through interaction and interweaving, a stable network structure is constructed, improving the long-term mechanical properties of the material.

[0019] 3) After freeze-thaw cycles are carried out under the harsh simulated actual service environment, the mass loss is only 1.66% after 10 cycles, showing stability, and the strength loss rate is only 3.95% after 10 cycles. 4) Studies conducted through electrochemical impedance spectroscopy (EIS) and industrial CT scanning have shown that the increase in porosity and pore number, as well as the degree of surface structure damage are significantly lower than those of conventional building materials, and the solidification system has excellent stabilization performance for red mud heavy metals (As, Hg, Pb, etc.). BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It represents the unconfined compressive strength of the sample prepared in Example 1.

[0021] Figure 2 It represents the unconfined compressive strength of the sample of red mud-steel slag binary cementitious material system.

[0022] Figure 3 It represents the unconfined compressive strength of the sample of the red mud-steel slag-fly ash ternary cementitious material system.

[0023] Figure 4 Represents the sample surface map, where a represents untreated, b represents after four freeze-thaw cycles, and c represents after ten freeze-thaw cycles.

[0024] Figure 5 Represents the tomograms of the industrial CT scans of the samples, where a represents untreated, b represents four freeze-thaw cycles, and c represents ten freeze-thaw cycles. DETAILED DESCRIPTION

[0025] The specific embodiments of the present invention are described in detail below. Example 1

[0026] A method for preparing a composite solidified red mud material for a salt-freeze coupled environment. In this embodiment, a sample of a red mud-steel slag-fly ash-phosphogypsum quaternary gel system is prepared, comprising the following steps: a. Raw material pretreatment Red mud, steel slag, fly ash and phosphogypsum are taken as raw materials and put into a mixer to be fully mixed. The red mud is selected from the red mud yard in Xiaoyi, Shanxi Province, and the steel slag, fly ash and phosphogypsum are from Yuanheng Water Purification Material Factory in Gongyi City, Henan Province. The chemical composition of the raw materials is shown in Table 1, and the addition amount of the raw materials is shown in Table 2, and the addition amount is calculated in parts; water is added according to a water-cement ratio of 0.3, and the stirring and mixing are continued to be uniform to obtain a mixture.

[0027]

[0028]

[0029] b. Static pressure forming Pour the mixture into a cylindrical specimen mold with a specification of Φ50 mm×H50mm, and use the jack static pressure method to press it into a cylindrical specimen with a compaction degree ≥96%.

[0030] c, Curing After demolding, weighing, and measuring the height, place it in a plastic-sealed bag for sealing, and cure it in an environment with a temperature of 20±2°C and a humidity ≥95% to ensure uniform humidity inside the sample and avoid rapid evaporation of moisture, thus obtaining the specimen.

[0031] Distribute the curing time of the specimens into 3 days, 7 days, and 28 days. After the curing period ends, take out the samples and use a YHS-229WJ-50kN microcomputer-controlled electronic universal testing machine produced by Shanghai Yihuan Instrument Technology Co., Ltd. to conduct an unconfined compressive strength (UCS) test with a testing speed of 1 mm / min. The compressive strength of the specimens prepared in Example 1 is as Figure 1 .

[0032] d, Salt-freezing coupling environment treatment The specimens after 28 days of curing are immersed in the salt solution for 24 hours, and a coupling salt solution with a concentration 10 times higher than the highest content of underground corrosion ions is prepared for the durability test of the solidified red mud. The salt solution includes 0.03 mol / L Na2SO4, 0.04 mol / L Na2CO3, and 0.05 mol / L NaCl, simulating the salt-freezing coupling environment. The liquid level is higher than the top surface of the specimen, and it is immersed for 4 days. The salt solution simulates the composite corrosion salt solution environment of the actual service environment, and then the specimens are placed in a freeze-thaw test chamber for freeze-thaw treatment. After the specimens are frozen in an environmental chamber with a temperature set at -23°C for 12h, they are taken out and melted in an environment at room temperature of 25°C for 12h. This is 1 freeze-thaw cycle, and the freeze-thaw cycle is carried out 2 - 10 times. The number of freeze-thaw cycles for each specimen group is selected as 2, 4, 6, 8, and 10 times respectively.

[0033] Comparative Example 1 Specimens of the red mud - steel slag binary cementitious material system and the red mud - steel slag - fly ash ternary cementitious material system are prepared by the method of equal substitution. Except for the raw materials, the remaining steps a - c are exactly the same as those in Example 1. The addition amounts of the raw materials are shown in Table 3, and the addition amounts are in parts; the compressive strength of the specimens prepared in Comparative Example 1 is as Figure 2 、 3 shown.

[0034]

[0035] The results of comparing Example 1 with Comparative Example 1 show that the compressive strength of the red mud-steel slag-fly ash-phosphogypsum quaternary cementitious system is improved compared with the red mud-steel slag-fly ash ternary cementitious material in Comparative Example 1. It can be seen that due to the use of phosphogypsum as a supplementary material and activator, the sulfate ions (SO4 2- ) promotes the formation of ettringite (AFt), which not only improves the early strength of the material, but also optimizes the entire hydration process. Specifically in the hydration reaction, SO4 2- It reacts with aluminosilicates to form calcium aluminum sulfate (AFm) phase, which further promotes the hydration reaction of aluminum and silicon, especially [AlO4] - and [SiO4] - The hydration products form a stable network structure through interaction and interweaving, thus improving the long-term mechanical properties of the material.

[0036] In addition, when the phosphogypsum content is less than 9 parts, the Ca 2+ It also participates in the geopolymerization process of sodium calcium aluminosilicate hydrate (NCSAH), further enhancing the stability of the cementitious structure. Example 2

[0037] A method for preparing a composite solidified red mud material for a salt-freeze coupled environment comprises the following steps: a. Raw material pretreatment 48.2 parts of red mud, 24.1 parts of steel slag, 8 parts of fly ash, 8.9 parts of phosphogypsum, 2.8 parts of chitosan, 4.1 parts of ultrafine quartz powder, and 3.9 parts of attapulgite are put into a blender as raw materials and mixed thoroughly; water is added according to a water-cement ratio of 0.3, and the mixture is stirred and mixed evenly to obtain a mixture; The remaining steps are exactly the same as those in Example 1.

[0038] During and after the salt-freeze coupled environmental treatment, the surface of the samples was observed for peeling, loose particles, cracking, and mud. The results showed that after the initial freeze-thaw, only local peeling and small cracks appeared on the surface of the samples. As the number of freeze-thaw cycles increased, only pits and flaking appeared. After 10 cycles, the overall structure was not affected, and the mass loss was only 1.66%, showing stability.

[0039] Industrial CT scanning technology was used to perform pore analysis on the samples.

[0040] Cut the specimen into a size suitable for scanning, ensuring a smooth surface; use a high-resolution industrial CT scanner with scanning parameters of 100 kV voltage, 100 μA current, and 0.5 μm / pixel resolution for 360-degree rotational scanning to obtain two-dimensional slice images; use the professional image processing software Avizo for three-dimensional reconstruction to generate a three-dimensional pore structure model; apply threshold segmentation technology to distinguish the solid part and the pore part, measure and count the volume and number of each pore through voxel analysis, and use the built-in pore analysis tool in the software to obtain the number of pores in different volume ranges.

[0041] As Figure 4 shown in a, before the specimen undergoes freeze-thaw treatment, the surface is smooth and tidy. However, after four freeze-thaw cycles, as Figure 4 shown in b, only irregular serrated shapes appear on the surface, becoming relatively rough, and no particle exposure occurs. When the number of freeze-thaw cycles reaches 10 times, as Figure 4 visible in c, the main structure is intact, and only local areas show controllable surface reconstruction phenomena, which fully demonstrates the anti-damage ability of the material matrix.

[0042] The mass loss rate of the specimen prepared in Example 2 is only 1.66% after 10 freeze-thaw cycles, the strength retention rate is as high as 96.05%, and the dynamic elastic modulus decreases limitedly, showing high structural stability. Compared with the existing technology, the enhanced recycled concrete has significant mass and strength attenuation under similar conditions, and the EPS cement soil also shows serious modulus degradation after freeze-thaw in a high-concentration salt environment. Although the PVA fiber concrete improves the performance to a certain extent, the overall freeze resistance stability is still inferior to this system.

[0043] This performance advantage is attributed to the synergistic effect among multi-component materials. Chitosan endows the organic enhancement effect and membrane wrapping characteristics in the system, ultrafine quartz powder improves the framework density and Si source supply, and the layered structure of attapulgite effectively adsorbs ions and delays migration. This synergistic mechanism jointly promotes the optimization of the pore structure, the inhibition of microcrack propagation, and the strengthening of the interfacial transition zone, thus significantly improving the comprehensive durability and service stability of the material in the salt freeze-thaw coupling environment. Overall, the composite mixing ratio scheme of the present invention shows performance improvements superior to the conventional system in terms of mechanics, durability, and microstructure, and has good engineering application and promotion prospects.

[0044] As Figure 5 shown, after the salt freeze-thaw treatment of the specimen, the number and volume of its internal pores increase significantly, and the specimen shows dynamic pore regulation characteristics during the freeze-thaw process. The porosity steadily increases from the initial 0.2920% to 0.5317%, and this orderly pore development mode provides an effective freeze-thaw buffer space for the material.

[0045] Referring to the national standard GB 5086.1-1997, a leaching experiment was conducted on the samples after 10 freeze-thaw cycles, with the liquid-solid ratio set at 10, the stirring frequency at 30 ± 2 r / min, and lasting for 18 hours. The leaching concentrations of elements such as Na, As, Hg, Zn, Pd, and Cu were detected by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0046] The results showed that the leaching concentrations of harmful elements in the samples all met the World Health Organization (WHO) standards for safe drinking water. This indicates that even under the influence of 10 freeze-thaw cycles, the synergistic effect of the raw materials can still effectively immobilize harmful elements. Therefore, the material prepared in this embodiment, as a green cementitious material with good frost resistance, can ensure its environmental safety and shows excellent potential in both environmental protection and engineering applications.

[0047] The scope of protection claimed in the present invention is not limited to the above specific embodiments, and for those skilled in the art, the present invention can have various deformations and modifications. Any modification, improvement, and equivalent replacement made within the concept and principle of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite solidified red mud material for salt-freezing coupling environment, characterized in that It includes 27~49 parts of red mud, 24~47 parts of steel slag, 8~19 parts of fly ash and 3~15 parts of phosphogypsum.

2. The composite solidified red mud material for salt-freezing coupling environment according to claim 1, characterized in that It includes 27~31 parts of red mud, 41~47 parts of steel slag, 17~19 parts of fly ash, and 3~15 parts of phosphogypsum.

3. A composite solidified red mud material for salt-freezing coupling environment according to claim 1, characterized in that, It also includes 2 to 5 parts of chitosan, 3 to 5 parts of ultrafine quartz powder, and 3 to 5 parts of attapulgite.

4. A composite solidified red mud material for salt-freezing coupling environment according to claim 3, characterized in that, It includes 48.2 parts of red mud, 24.1 parts of steel slag, 8 parts of fly ash, 8.9 parts of phosphogypsum, 2.8 parts of chitosan, 4.1 parts of ultrafine quartz powder, and 3.9 parts of attapulgite.

5. A preparation method of a composite solidified red mud material for a salt-freezing coupling environment, characterized in that, The following steps are involved: a. Raw material pretreatment Take red mud, steel slag, fly ash and phosphogypsum as raw materials and put them into a mixer to mix them thoroughly; add water according to a water-cement ratio of 0.3, continue to stir and mix evenly to obtain a mixture; b. Static pressure forming Pour the mixture into a cylindrical specimen mold and press it into a cylindrical specimen using a jack static pressure method, with a compaction degree of ≥96%; c. Maintenance After demoulding, weighing and measuring, place in a plastic bag, seal it, and place it in an environment with a temperature of 20±2℃ and a humidity of ≥95% for curing to obtain a sample; d. Salt-freeze coupled environment treatment After curing, the specimens were immersed in a salt solution for 24 hours, wherein the salt solution included 0.02-0.05 mol / L Na2SO4, 0.03-0.06 mol / L Na2CO3, and 0.04-0.07 mol / L NaCl, simulating a salt-freeze coupling environment. The liquid level was higher than the top surface of the specimens, and then the specimens were taken out for freeze-thaw treatment.

6. The preparation method of a composite solidified red mud material for a salt-freezing coupling environment according to claim 5, characterized in that, The raw materials in step a also include chitosan, ultrafine quartz powder and attapulgite.

7. The preparation method of a composite solidified red mud material for a salt-freezing coupling environment according to claim 5, characterized in that, In step a, the raw materials include 48.2 parts of red mud, 24.1 parts of steel slag, 8 parts of fly ash, 8.9 parts of phosphogypsum, 2.8 parts of chitosan, 4.1 parts of ultrafine quartz powder, and 3.9 parts of attapulgite.

8. The preparation method of a composite solidified red mud material for a salt-freezing coupling environment according to claim 5, wherein The freeze-thaw process comprises the following steps: The sample is placed in an environmental box set at -25℃~-15℃ for freezing for 8~14 hours, then taken out and placed at room temperature 15~30℃ for thawing for 8~14 hours as one freeze-thaw cycle, and the freeze-thaw cycles are repeated 2~10 times.

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