Method for regulating and controlling volume stability of steel slag by activating siliceous mine tailings

Abstract

The invention discloses a method for regulating and controlling the volume stability of steel slag by activating siliceous mine tailings, which comprises the following steps: carrying out alkali heat activation treatment on the siliceous mine tailings by taking alkaline red mud as a main alkali source, enhancing the release of active silicon monomers from the tailings, eliminating f-CaO in the steel slag, and converting the steel slag into C-S-H gel with stable volume and gelling activity. The steel slag-based cementing material prepared from the activated tailings and the steel slag is good in volume stability and relatively high in compressive strength. The method can effectively reduce the restriction effect of traditional steel slag pretreatment, and directly realizes the safe application of the steel slag in the cementing material. Meanwhile, the method also realizes synergistic resource utilization of various bulk solid wastes such as the steel slag, the siliceous mine tailings and the alkaline red mud, and meets the strategic requirements of sustainable development.

Description

Technical Field

[0001] The invention relates to the technical field of steel slag volume stability control, and in particular to a method for controlling the volume stability of steel slag by activating siliceous mine tailings. Background Art

[0002] As the world's largest steel producer, my country's annual steel slag emissions exceed 100 million tons, but the utilization rate is only about 30%. The chemical and mineral composition of steel slag is similar to that of ordinary Portland cement clinker. It is expected to be widely used in the field of building materials, just like other industrial solid wastes such as blast furnace slag and fly ash. However, the current utilization rate of steel slag in the field of building materials in my country is only 22%. The instability of steel slag volume is an important reason for this result. f -CaO undergoes hydration reaction to generate Ca(OH)2 crystals, resulting in volume expansion that can cause structural cracks in building materials, seriously affecting their safety and service life. In order to eliminate the negative impact of steel slag volume expansion on building materials, f -CaO content must be strictly controlled below 2%. However, according to statistics, about 50% of the steel slag discharged by my country's steel enterprises contains f -CaO content is higher than 2%, which cannot meet the requirements of its use in the field of building materials. f -CaO regulating the volume stability of steel slag is still a technical bottleneck that needs to be overcome in the utilization of steel slag as building materials.

[0003] At present, steel slag f -CaO elimination and transformation methods mainly include natural aging, mechanical grinding, high temperature reconstruction and carbonization treatment. However, the four typical process methods currently in use all require specific pretreatment procedures, which will undoubtedly increase the difficulty of treating and utilizing steel slag, making it difficult to achieve such a large-scale pretreatment of steel slag in China. Based on the theory of alkali-induced hydration reaction of cementitious materials: the active silicon monomers released by the dissolution of active raw materials undergo dehydration and polycondensation in alkaline solution to form oligomeric silicate ions, which, under the action of electrostatic attraction, bind to the Ca in the system. 2+ Finally, a stable calcium silicate hydrate (CSH) gel with gelling properties is generated. It can be seen that the alkali-activated gelling material produced by the synergistic production of steel slag and active siliceous raw materials can achieve the goal of f -CaO in situ elimination and transformation, reducing the restrictive effect of steel slag pretreatment, has significant development and application value. Siliceous tailings are the main type of mine tailings in my country (mainly composed of SiO2), which has the effect of eliminating and transforming the steel slag. f -CaO research basis. However, the tailings structure is stable and difficult to dissolve and release active silicon monomers under normal temperature and alkaline environment. Therefore, strengthening the release of active silicon monomers from siliceous tailings is the key to achieving the elimination and transformation of siliceous tailings. f-CaO is a prerequisite for regulating the volume stability of steel slag. Currently, alkali fusion is the most effective tailings activation technology, but high-temperature calcination (600°C–1000°C) is inevitably accompanied by huge energy consumption and expensive activation costs. Therefore, it is necessary to develop a more economical new tailings activation technology.

[0004] According to relevant reports on the synthesis of functional materials from tailings, alkaline medium hydrothermal technology (abbreviated as "alkali thermal activation") can significantly improve the leaching rate of active silicon monomers. However, a large amount of NaOH will be consumed in the process of alkali thermal activation of tailings (the amount of NaOH usually needs to be controlled at 20-30% of the mass of the tailings), which is the main cost factor for tailings activation. Therefore, it is of great significance to develop a widely available and low-cost alkali source to partially or even completely replace NaOH to reduce the economic cost of activating siliceous tailings. Red mud is a typical bulk solid waste generated by the alumina production industry. It has the characteristics of high alkalinity, fine particle size and complex composition. At present, the utilization rate of red mud in my country is less than 10%. Based on the characteristics of high free alkali content in red mud, it is technically feasible to use red mud as the main alkali source to carry out alkali thermal activation of siliceous tailings to enhance the release of active silicon monomers from siliceous tailings. Therefore, using red mud as the main alkali source to carry out alkali thermal activation of siliceous tailings, enhance the release of active silicon monomers from siliceous tailings to eliminate the conversion of steel slag. f -CaO is a new, economical and efficient method for regulating the volume stability of steel slag. It can also realize the resource utilization of difficult-to-treat bulk solid wastes such as red mud, tailings, and steel slag in the field of cementitious materials, which is in line with the requirements of the national sustainable development strategy. However, there are currently few reports on this aspect.

[0005] Therefore, it is necessary to propose further solutions to the above problems. Summary of the Invention

[0006] The present invention aims to provide a method for activating siliceous mine tailings to control the volume stability of steel slag, and at the same time realize the resource utilization of red mud, siliceous tailings and steel slag in the field of cementitious materials. Red mud is used as the main alkali source to activate siliceous tailings to release active silicon monomers, eliminate free calcium oxide ( f -CaO), thereby regulating the volume stability of steel slag.

[0007] The technical solution of the present invention is: A method for activating siliceous mine tailings to control the volume stability of steel slag, the method comprising the following steps: Step 1: First, 20 g of red mud and 80 g of siliceous mine tailings were stirred in 100 mL of a 50 g / L NaOH solution to form a uniform slurry. The mixed slurry was then transferred to a 200 mL hydrothermal reactor and heated at 200°C for 4 hours. After the reaction, the mixture was cooled to room temperature and dried in a vacuum oven. The dried sample was further ground into a powder to obtain the activated siliceous mine tailings, referred to as the activated tailings.

[0008] Step 2: Mix the activated tailings and steel slag powder in a mass ratio of 30%:70%. Then, stir the mixture with tap water at a water-to-solid ratio of 0.5 (mass ratio). Pour the mixture into a 4 × 4 × 4 cm silicone mold and cure it in a standard constant temperature and humidity curing chamber to obtain a steel slag-based cementitious material with excellent volume stability. Furthermore, the stirring in step 1 is performed at room temperature for 10 minutes.

[0009] Furthermore, the drying in step 1 should be carried out at 100° C. until the sample reaches a constant weight.

[0010] Furthermore, the particle size of the powdered sample in step 1 is ≤ 74 μm.

[0011] Furthermore, the stirring in step 2 is carried out at room temperature in a cement slurry mixer for 5 minutes.

[0012] Furthermore, the curing in step 2 is performed at a temperature of 20° C. and a relative humidity ≥ 90%.

[0013] Furthermore, the volume stability described in step 2 is the technical standard established in the national standard GB / T 1346-2024.

[0014] The present invention provides a method for activating siliceous mine tailings to regulate the volume stability of steel slag. First, red mud is used as the main alkali source, supplemented by a small amount of NaOH as a supplementary alkali source, and the inert siliceous tailings are subjected to alkali thermal activation treatment at 200 °C. During the alkali thermal activation process, under the erosion of the alkaline medium, the crystal structure of the silicate phase in the siliceous tailings is destroyed and converted into an cryptocrystalline, alkaline activation product. The product has good solubility, can dissolve a large amount of active silicon monomers in water, and create a higher alkaline environment. The alkali thermal activation technology can significantly improve the leaching rate of active silicon monomers in siliceous tailings. Compared with the traditional alkali fusion method, this method has a lower activation temperature (200 °C); at the same time, alkaline red mud is used as the main alkali source in the alkali thermal activation process, which further reduces the activation cost. On this basis, the activated tailings powder, steel slag powder and water are directly mixed to prepare steel slag-based cementitious materials. The experimental results show that during the hydration process of the cementitious material, the active silicon monomers released by the dissolution of the active tailings react with the active silicon monomers in the steel slag. f -CaO undergoes hydration reaction to form CSH gel with gelling activity. Therefore, steel slag-based cementitious materials can maintain good volume stability and exhibit high compressive strength, showing good application potential in the field of cementitious materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic flow chart of a method for controlling the volume stability of steel slag by activating siliceous mine tailings according to the present invention; Figure 2 This is an SEM image of the method for controlling the volume stability of steel slag by activating siliceous mine tailings according to the present invention. Figure 2 (a) is the SEM image of the original siliceous tailings, Figure 2 (b) is the SEM image of activated siliceous tailings; Figure 3 In the method for regulating the volume stability of steel slag by activating siliceous mine tailings of the present invention, the XRD patterns of the original siliceous tailings and the activated siliceous tailings ( Figure 3 (a) FTIR spectrum ( Figure 3 (b) Si in its leachate 4+ The concentration ( Figure 3 (c)); Figure 4 The compressive strength of the steel slag-based gelling material in the method for controlling the volume stability of steel slag by activating siliceous mine tailings of the present invention; Figure 5 This is the test result of the volume stability of steel slag-based gelling material in the method of regulating the volume stability of steel slag by activating siliceous mine tailings of the present invention. Figure 5 (a) is the expansion value of the material before boiling, Figure 5 (b) is the expansion value of the material after boiling; Figure 6 In the method for controlling the volume stability of steel slag by activating siliceous mine tailings of the present invention, the XRD pattern of the steel slag-based cementitious material after curing for 3 days ( Figure 6 (a)) and XRD patterns after curing for 28 days ( Figure 6 (b)); Figure 7 This is an SEM image of the steel slag-based cementitious material cured for 28 days in the process of controlling the volume stability of steel slag by activating siliceous mine tailings according to the present invention. Figure 7 (a) is the control group, Figure 7 (b) is the experimental group. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below with reference to specific embodiments. In the accompanying drawings, the control group is a cementitious material prepared from 100% steel slag, and the experimental group is a cementitious material prepared from 30% activated tailings + 70% steel slag.

[0017] See also Figure 1 , Figure 1 The figure is a flow chart of the method for controlling the volume stability of steel slag by activating siliceous mine tailings according to the present invention. Figure 1 As shown, the present invention provides a method for activating siliceous mine tailings to control the volume stability of steel slag, comprising the following steps: The main components of the red mud used in the present invention are: 40.35% Fe2O3, 17.56% Al2O3, 14.24% SiO2, and 9.24% Na2O.

[0018] The main components of siliceous mine tailings are: 71.28% SiO2, 15.68% Al2O3, 3.12% Na2O, and 5.05% K2O.

[0019] The main components of steel slag powder are: 19.25% SiO2, 7.25% Al2O3, 42.94% CaO, 7.26% MgO, and 18.67% Fe2O3.

[0020] Step 1: First, 20 g of red mud and 80 g of siliceous mine tailings were stirred in 100 mL of a 50 g / L NaOH solution at room temperature for 10 minutes to obtain a uniform slurry. The mixed slurry was then transferred to a 200 mL hydrothermal reactor and heated at 200°C for 4 hours. After the reaction, the mixture was cooled to room temperature and dried in a vacuum drying oven at 100°C. The dried sample was further ground into a powder with a particle size of ≤ 74 μm, resulting in activated siliceous mine tailings, also known as activated tailings.

[0021] Step 2: Mix the activated tailings and steel slag powder in a mass ratio of 30%:70%. Then, stir the mixture with tap water in a cement slurry mixer at room temperature for 5 minutes at a water-to-solid ratio of 0.5 until uniform. Pour the resulting mixture into a 4 × 4 × 4 cm silicone mold and cure it in a standard constant temperature and humidity curing chamber at 20°C and a relative humidity of ≥ 90%. This yields a steel slag-based cementitious material with excellent volume stability (as specified in the national standard GB / T 1346-2024).

[0022] After the above two steps, a steel slag-based cementitious material with good volume stability is obtained. After these two steps, the hydration reaction characteristics of the steel slag-based cementitious material are further analyzed and tested.

[0023] Step 3: Use X-ray diffraction technology and scanning electron microscopy to analyze the hydration products and micromorphology of steel slag-based cementitious materials to reveal the regulatory mechanism of activated siliceous tailings on the volume stability of steel slag.

[0024] The abbreviations mentioned in the present invention are all fixed abbreviations in this field, and some of the abbreviations are explained as follows: SEM: scanning electron microscope; FTIR: Fourier transform infrared spectroscopy; XRD: X-ray diffraction pattern; ICP: inductively coupled plasma spectrometer.

[0025] Example 1 This implementation case shows the implementation plan of alkali thermal activation of siliceous mine tailings according to the following scheme.

[0026] In order to characterize the activated siliceous tailings, the present invention uses SEM, XRD, FTIR and ICP testing methods to analyze the micromorphology, relative crystallinity, polymer structure and leaching rate of active silicon monomers of the activated tailings.

[0027] See also Figure 2 The original tailings particles have a smooth surface with obvious sharp edges and corners. However, after alkali-thermal activation, the sharp edges and corners of the tailings particles disappear. At the same time, a large amount of gel-like products are found covering the surface of the activated tailings particles, and the overall microscopic appearance is relatively rough. This result shows that the structure of the mine tailings has been destroyed. Figure 3 From the XRD spectrum, it can be seen that after alkali thermal activation, the diffraction peak intensity of the main mineral phases such as quartz, albite, microcline, and mica in the tailings is significantly weakened, the relative crystallinity is reduced, and the degree of amorphization is increased, so the reaction activity of the tailings is enhanced. In the FTIR spectrum, at the wave number of 3400 cm -1 and 1600cm -1The absorption peaks near the wave number 1440 cm correspond to the bending vibration of -OH and HOH bonds in water molecules. The intensity of these two absorption peaks in the activated tailings is significantly stronger than that in the original tailings. This is because the activation products containing water are generated during the alkali-thermal activation of the tailings. -1 The absorption peak near the tailings corresponds to the symmetrical stretching vibration of the OCO bond in the carbonate phase. The intensity of this peak in the activated tailings is significantly higher than that in the original tailings, indicating that the phase in the tailings reacted with CO2 during the alkali-thermal activation process. The wave number is 1020 cm -1 The absorption peak near the tailings corresponds to the asymmetric stretching vibration of the Si-O-Si (Al) bond in the aluminosilicate phase. Compared with the original tailings, the wave number of this peak in the activated tailings is lower, indicating that the polymeric structure of the aluminosilicate phase in the tailings is decomposed and converted into a new aluminosilicate phase with a lower degree of polymerization. The ICP test results show that after alkali thermal activation, the active Si in the activated tailings is 4+ The leaching concentration was significantly increased to 4764 mg / L. Combining the test results of SEM, XRD, FTIR and ICP, it can be seen that during the alkali thermal activation process with red mud as the main alkali source and a small amount of NaOH as a supplementary alkali source, the stable crystal structure of the tailings was destroyed, and the main mineral phases such as quartz, albite, microcline, and mica in the tailings reacted with the alkali source to form a low-polymerization aluminosilicate activation product, which is easily soluble in water and can release a large amount of active Si 4+ .

[0028] The alkali-thermal activation technology described in this invention can effectively activate inert siliceous mine tailings and enhance the release of silicon monomers from the tailings. The activation temperature of this alkali-thermal method can be controlled at around 200°C, significantly lower than the traditional alkali fusion method (above 600°C). Furthermore, this method uses red mud, an alkaline solid waste, as the primary alkali source, further reducing the cost of tailings activation and providing significant economic and environmental benefits.

[0029] Example 2 This implementation case demonstrates the implementation plan for regulating the volume stability of steel slag by alkali-thermal activation of siliceous mine tailings according to the following scheme.

[0030] The present invention uses activated tailings fine powder (30%) and steel slag fine powder (70%) as main raw materials, controls the water-solid ratio to 0.5 (mass ratio), prepares steel slag-based cementitious material, and analyzes its compressive strength and volume stability.

[0031] See also Figure 4The compressive strength of the control group was extremely low, and it could not harden after 3 and 7 days of curing. Even if the curing time was extended to 28 days, its compressive strength was only 1.53MPa. Compared with the control group, the compressive strength of the experimental group was significantly improved, and its compressive strength after curing for 3, 7 and 28 days reached 3.22, 5.88 and 10.91MPa respectively. Furthermore, in accordance with GB / T 1346-2024 "Test Method for Water Consumption, Setting Time and Stability of Cement Standard Consistency", the volume stability of the steel slag-based cementitious material in the experimental group was tested using a Levitra dilatometer. The test results are available at Figure 5 The results show that the expansion value of the cementitious material before boiling is A =13 mm, expansion value of the cementitious material after boiling C =15 mm, the difference in expansion value of the cementitious material before and after boiling is less than 3 mm, and its volume stability meets the technical requirements of the national standard GB / T 1346-2024.

[0032] The method of regulating the volume stability of steel slag by alkali-thermal activation of siliceous mine tailings, which is disclosed in the present invention, effectively avoids the pretreatment of steel slag and greatly reduces the restrictive effects of complex processes and high costs caused by the pretreatment of steel slag. It can realize the direct application of steel slag in cementitious materials, which is of great significance for improving the resource utilization rate of steel slag. At the same time, the method of regulating the volume stability of steel slag by activating siliceous mine tailings disclosed in the present invention simultaneously realizes the coordinated resource utilization of three difficult-to-treat bulk industrial solid wastes, namely steel slag, siliceous mine tailings, and alkaline red mud, providing a new idea for the coordinated treatment of multiple solid wastes and meeting the requirements of the sustainable development strategy.

[0033] Example 3 This implementation case demonstrates the implementation plan of the control mechanism of alkali-thermal activation of siliceous mine tailings on the volume stability of steel slag according to the following scheme.

[0034] The present invention further utilizes XRD and SEM techniques to analyze the hydration products and micromorphology of steel slag-based gelling materials, revealing the regulating mechanism of activated siliceous tailings on the volume stability of steel slag.

[0035] See also Figure 6 It can be clearly observed that the diffraction peaks of calcium hydroxide (Ca(OH)2, 2θ≈18°, 34° and 46°) can be observed in the XRD patterns of the control group after hydration for 3 days and 28 days, indicating that the diffraction peaks of calcium hydroxide (Ca(OH)2, 2θ≈18°, 34° and 46°) in the steel slag are f -CaO reacts with H2O to produce Ca(OH)2, fThe volume expansion caused by the conversion of -CaO to Ca(OH)2 crystals is the main reason for the volume instability of steel slag. Compared with the control group, no diffraction peak of Ca(OH)2 phase was found in the XRD patterns of the experimental group after hydration for 3 days and 28 days. This is because the active silicon monomers released by the activated tailings during the hydration reaction convert the active silicon monomers in the steel slag into f -CaO is eliminated in time and converted into CSH gel with stable volume and gelling activity. Therefore, the volume stability of the experimental group meets the requirements and shows high compressive strength. Figure 7 In the SEM images of the control group, the presence of flaky Ca(OH)2 products can be clearly observed, while in the SEM images of the experimental group, no Ca(OH)2 products were found. At the same time, a large amount of amorphous CSH gel can be observed covering the surface of the raw material particles, gluing them into a dense whole. The SEM analysis results further prove that the active silicon monomers released by the activated tailings can convert the active silicon monomers in the steel slag into f -CaO elimination and conversion into CSH gel.

[0036] Comparative Example 1 The difference from the preparation method of the present invention is that the mixing and heating methods of the red mud and tailings in step 1 are different.

[0037] Step 1: First, 20 g of red mud and 80 g of siliceous mine tailings were mechanically stirred with NaOH for 10 minutes. The mixture was then dry-milled in a ball mill for 25 minutes to produce a milled material. The milled material was heated in a kiln at 200°C for 4 hours. After the reaction, the material was cooled to room temperature and dried in a vacuum oven at 100°C. The dried sample was further ground into a powder with a particle size of ≤ 74 μm, yielding the activated tailings.

[0038] Step 2: Mix the activated tailings and steel slag powder in a mass ratio of 30%:70%. Then, stir the mixture with tap water in a cement slurry mixer at room temperature for 5 minutes at a water-to-solid ratio of 0.5 until uniform. Pour the mixture into a 4 × 4 × 4 cm silica gel mold and cure it in a standard constant temperature and humidity curing chamber at 20°C and a relative humidity of ≥ 90% to obtain the steel slag-based cementitious material.

[0039] Comparing the cementitious material of Comparative Example 1 with the cementitious material prepared by the preparation method of the present invention, the compressive strength of the present invention is significantly improved, and the compressive strength after curing for 3 days, 7 days and 28 days reaches 3.22, 5.88 and 10.91 MPa, respectively, while the compressive strength of the cementitious material in Comparative Example 1 is significantly reduced, and the compressive strength after curing for 3 days, 7 days and 28 days reaches 0.34, 0.74 and 1.69 MPa, respectively.

[0040] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiment based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for regulating the volume stability of steel slag by activating siliceous mine tailings, characterized in that: The steps include: Step 1: First, 20 g of red mud and 80 g of siliceous mine tailings were stirred in 100 mL of 50 g / L NaOH solution to obtain a uniform slurry; then, the mixed slurry was transferred to a hydrothermal reactor and heated at 200 °C for 4 h; after the reaction was completed, it was cooled to room temperature and the mixed slurry was placed in a vacuum drying oven for drying; the dried sample was ground into a powder sample to obtain activated siliceous mine tailings, namely activated tailings. Step 2: Mix the activated tailings and steel slag powder in a mass ratio of 30%:70%, and then stir the activated tailings-steel slag powder mixture with tap water at a water-solid mass ratio of 0.5; then, pour the evenly stirred fresh slurry into a silica gel mold and cure it in a standard constant temperature and humidity curing box to obtain a steel slag-based cementitious material with good volume stability.

2. The method for controlling the volume stability of steel slag by activating siliceous mine tailings according to claim 1, characterized in that: The stirring in step 1 is stirring at room temperature for 10 min.

3. The method for controlling the volume stability of steel slag by activating siliceous mine tailings according to claim 1, characterized in that: The drying step in step 1 should be performed at 100°C until the sample reaches a constant weight.

4. The method for controlling the volume stability of steel slag by activating siliceous mine tailings according to claim 1, characterized in that: The particle size of the powdered sample in step 1 is ≤ 74 μm.

5. The method for controlling the volume stability of steel slag by activating siliceous mine tailings according to claim 1, characterized in that: The stirring in step 2 is: stirring in a cement slurry mixer at room temperature for 5 minutes.

6. The method for controlling the volume stability of steel slag by activating siliceous mine tailings according to claim 1, characterized in that: The curing in step 2 is performed at a temperature of 20°C and a relative humidity of ≥ 90%.

7. Application of the method for regulating the volume stability of steel slag by activating siliceous tailings according to any one of claims 1 to 6 in the field of cementitious materials.

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