Method for enhancing hydration activity of steel slag by using red mud activated siliceous tailings as siliceous modifier

Abstract

The invention discloses a method for enhancing hydration activity of steel slag by using red mud activated siliceous tailings as a siliceous modifier, and belongs to the technical field of steel slag modification. The method comprises the following steps: (1) adding deionized water into red mud, NaOH and siliceous tailings, and reacting after uniformly stirring; after the reaction is finished, cooling reactants to room temperature, drying and grinding to obtain activated tailings; (2) mixing the activated tailings with steel slag, adding deionized water, and carrying out oscillation reaction; after the reaction is finished, centrifuging to obtain a solid product; and washing, centrifuging, drying and grinding the solid product to obtain the modified steel slag. According to the method, the red mud is firstly adopted to activate the siliceous tailings to obtain the activated tailings, then the steel slag is modified, a C-S-H product is generated on the surface of the steel slag, the hydration activity of the steel slag is remarkably enhanced, the 3-day activity index and the 28-day activity index of the steel slag can reach 81.16% and 100.62%, and resource utilization of the red mud, the tailings and the steel slag is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel slag modification, and particularly relates to a method for activating siliceous tailings as siliceous modifiers to enhance the hydration activity of steel slag. BACKGROUND

[0002] In recent years, with the rapid development of China's steel industry, the discharge amount of steel slag solid waste increases year by year, but the utilization rate is low, and the economic and environmental problems caused by the storage of a large amount of steel slag have attracted widespread attention. The chemical composition and mineral composition of steel slag are similar to those of ordinary Portland cement clinker, and have certain potential cementitious activity, so that steel slag has broad application prospects in the field of building materials. However, compared with blast furnace slag, silica ash and other industrial solid wastes, the glass structure content of steel slag is relatively low, resulting in low hydration reaction activity of steel slag, and some steel slag even does not have hydration reaction activity. In order to enhance the hydration activity of steel slag, it is usually necessary to activate and pretreat the steel slag, and mechanical grinding is the most commonly used activation technology. After grinding, the specific surface area of steel slag increases, the effective hydration reaction area of steel slag particles increases, and the hydration reaction rate accelerates, thereby improving the hydration reaction activity of steel slag. However, mechanical grinding is an energy-intensive process, and the steel slag has high hardness and strong wear resistance. In order to grind the steel slag to a fineness sufficient to significantly improve the activity, a large amount of electric energy needs to be consumed, resulting in a sharp rise in processing cost, which may sometimes even offset the economic benefits brought by the use of cheap solid waste, which is contrary to the environmental protection idea of "green and low carbon". Therefore, developing an economic and effective technical means to enhance the hydration reaction activity of steel slag and improve the utilization rate of steel slag in the field of building materials has become a problem to be solved. SUMMARY

[0003] Based on the above technical problems, the application provides a method for activating siliceous tailings as siliceous modifiers to enhance the hydration activity of steel slag.

[0004] The technical solution adopted by the application is as follows: The method for activating siliceous tailings as siliceous modifiers to enhance the hydration activity of steel slag comprises the following steps: a, preparing activated tailings; a1, mixing the red mud and the siliceous tailings after grinding, and then adding NaOH particles and stirring uniformly to obtain a mixed powder; the above step is to ensure that the alkaline component and the siliceous component can be uniformly dispersed; a2, adding deionized water to the mixed powder obtained in step a1 and transferring to a high-speed shearing stirrer for stirring to obtain a mixed paste; and adding deionized water to the mixed paste, switching the high-speed shearing stirrer to a magnetic stirring mode for stirring to obtain a first mixed slurry; a3, transferring the first mixed slurry obtained in step a2 into a reaction kettle for reaction; after the reaction is completed, the obtained reaction product is cooled to room temperature, dried and ground into powder to obtain the activated tailings; b, preparing modified steel slag; b1, mixing the steel slag after grinding with the activated tailings obtained in step a3, adding deionized water, and then transferring into a vortex oscillator for pre-oscillation to obtain a second mixed slurry; the above step is to ensure that all powders are fully wetted and initially dispersed to form a uniform mixed system; b2, transferring the second mixed slurry obtained in step b1 into a constant temperature oscillation box for oscillation reaction; the oscillation step ensures that the slurry is always in a uniform suspended state and realizes the effect of mass transfer intensification; after the oscillation reaction is completed, centrifugal treatment is performed to obtain a solid product; b3, washing and centrifuging the solid product obtained in step b2 with deionized water to remove residual OH - and Na + , and then drying and grinding into powder to obtain the modified steel slag.

[0005] Preferably, in step a: the amount ratio of red mud, NaOH, siliceous tailings and deionized water is 18-22 g:4-6 g:65-75 g:90-110 g; wherein the deionized water is added twice in step a2, and the amount ratio of the first and second time is 0.9-1.1:0.9-1.1.

[0006] Preferably, step a2 specifically comprises the following steps: adding deionized water to the mixed powder obtained in step a1 and transferring into a high-speed shearing mixer for stirring, the stirring rate is 8000-12000 rpm, the stirring time is 3-5 min, to obtain a mixed paste; the above step is to use high-speed shearing force to completely break the particle agglomerates and make them fully wetted by the liquid phase; adding deionized water to the mixed paste, and switching the high-speed shearing mixer to a magnetic stirring mode for stirring, the stirring rate is 300-500 rpm, the stirring time is 25-35 min, to obtain a first mixed slurry; the above step is to maintain the uniform state of the slurry and prevent the particles from precipitating too fast.

[0007] Preferably, in step a3: the reaction temperature is 190-210 ℃, the time is 3.5-4.5 h; the drying temperature is 90-110 ℃, and the particle size range of the powder is less than 74 μm.

[0008] Preferably, in step b1: the amount ratio of activated tailings, steel slag and deionized water is 8-12 g:35-45 g:140-160 g.

[0009] Preferably, in step b1, the pre-oscillation time is 2-3 min.

[0010] Preferably, in step b2, the reaction temperature of the constant-temperature oscillation box is set to 20-30 ℃, the rotation speed is 170-190 r / min, and the reaction time is 23-25 h; the rotation speed of centrifugation is 3500-4500 r / min, and the time is 2-4 min.

[0011] Preferably, in step b3, the pH value of the supernatant after washing is 10.0-10.5, and the conductivity is less than 150 μS / cm; the drying temperature is 45-55 ℃, and the particle size range of the powder is less than 74 μm.

[0012] Preferably, step b3 specifically comprises the following steps: adding deionized water to the solid product obtained in step b2, then placing it in a vortex shaker to re-disperse the solid product in deionized water for washing, and then centrifuging to discard the supernatant, repeating the above "washing-centrifugation" process until the pH value of the supernatant after washing is stable between 10.0-10.5 and the conductivity is reduced to less than 150 μS / cm, which can be considered that the impurity ions (OH - and Na + ) have been basically removed; after the washing and centrifugation are completed, the solid product is dried and ground into powder to obtain the modified steel slag.

[0013] Preferably, the chemical composition of the red mud includes, in mass percentage: Fe2O332-38%, Al2O318-20%, SiO215-17%, and Na2O 7-9%; the chemical composition of the siliceous tailings includes: SiO270-75%, Al2O312-15%, Na2O 3-4%, and K2O 4-6%; and the chemical composition of the steel slag includes: CaO 43-47%, SiO2 20-23%, Al2O3 5-7%, and Fe2O315-18%.

[0014] In a specific embodiment, the chemical composition of the red mud includes, in mass percentage: Fe2O335.14%, Al2O318.46%, SiO216.03%, and Na2O 8.05%; the chemical composition of the siliceous tailings includes: SiO273.55%, Al2O313.57%, Na2O 3.43%, and K2O 4.86%; and the chemical composition of the steel slag includes: CaO 45.63%, SiO221.36%, Al2O36.34%, and Fe2O316.27%.

[0015] Preferably, the modified steel slag obtained by the above method is mixed with 42.5 Portland cement at a mass ratio of 3:7, uniformly stirred in a mortar mixer according to a water-cement ratio of 0.5 and a cement-sand ratio of 1:3 to obtain a mixed slurry; the compressive strengths of the mixed slurry cured for 3 days, 7 days and 28 days reach 18.95 MPa, 28.91 MPa and 45.56 MPa respectively, and the corresponding activity indexes reach 81.16%, 92.63% and 100.62% respectively. In the water-cement ratio and the cement-sand ratio, the cement refers to the total amount of the modified steel slag and the 42.5 Portland cement.

[0016] The beneficial technical effects of the present application are as follows: The present application modifies the steel slag by activating the tailings, generates C-S-H products on the surface of the steel slag, and significantly enhances the hydration activity of the steel slag; at the same time, realizes the collaborative resource utilization of the steel slag, siliceous mine tailings and alkaline red mud, and provides a new idea for the collaborative treatment of multiple solid wastes, which meets the requirements of the sustainable development strategy.

[0017] Specifically: (1) The siliceous tailings used in the present application have a high SiO2 content, and are matched with the specific component of the red mud, so that a small amount of NaOH can be added to prepare a siliceous modifier with high activity; (2) The activated tailings prepared in the present application have good solubility and can dissolve in water to release a large amount of active silicon monomers and create a high alkaline environment; at the same time, the alkaline red mud is used as the main alkali source, which realizes the full utilization of the red mud, greatly reduces the consumption of NaOH, significantly reduces the alkali-thermal activation cost of the tailings, has significant economic and environmental benefits, and realizes deeper utilization of "waste treatment with waste"; (3) The modified steel slag prepared in the present application is mixed in 42.5 Portland cement, and the compressive strengths of the modified steel slag cured for 3 days, 7 days and 28 days reach 18.95 MPa, 28.91 MPa and 45.56 MPa respectively, and the corresponding activity indexes reach 81.16%, 92.63% and 100.62% respectively, and the 28-day activity index is much higher than the requirement (65%) of GB 2847-2005 "Volcanic Ash Mixed Materials for Cement"; at the same time, compared with the 42.5 Portland cement mixed with unmodified steel slag, the compressive strength and activity index are significantly improved; (4) The present application generates network-shaped and porous C-S-H products on the surface of the steel slag particles, increases the specific surface area of the steel slag, provides nucleation sites for cement hydration, reduces the nucleation potential barrier of the hydration products, and accelerates the hydration process of the cement, thereby significantly enhancing the hydration activity of the steel slag; (5) The modification process of the present application does not need to add an activator, thereby reducing the cost of steel slag activation; at the same time, compared with the traditional mechanical grinding method, the modification process can be spontaneously carried out at room temperature, the activation cost is greatly reduced, and the application potential of steel slag in the building material field is greatly improved; (6) Based on the theory of pozzolanic reaction, the present application first modifies one kind of solid waste (red mud) to another kind of solid waste (siliceous tailings) to obtain a siliceous modifier, and then reacts with a third kind of solid waste (steel slag) to directionally generate a specific hydration product (C-S-H) to change the properties of the steel slag, which is more targeted. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 XRD patterns, FTIR patterns and concentrations of Si 4+ and Al 3+ in leaching solution of unactivated tailings and activated tailings in example 1 of the present application; wherein (a) is the XRD pattern, (b) is the FTIR pattern, and (c) is the concentration of Si 4+ and Al 3+ in leaching solution; Figure 2 XRD patterns and FTIR patterns of unmodified steel slag and modified steel slag in example 1 of the present application; wherein (a) is the XRD pattern, and (b) is the FTIR pattern; Figure 3 SEM images and EDS energy spectrum of unmodified steel slag and modified steel slag in example 1 of the present application; wherein (a) is the SEM image and EDS energy spectrum of unmodified steel slag, and (b) is the SEM image and EDS energy spectrum of modified steel slag; Figure 4 Pore size distribution curve and cumulative pore volume curve of unmodified steel slag and modified steel slag in example 1 of the present application; wherein (a) is the pore size distribution curve, and (b) is the cumulative pore volume curve; Figure 5 Compressive strength and activity index of mortar samples respectively mixed with unmodified steel slag and modified steel slag in example 1 of the present application; wherein (a) is the compressive strength, and (b) is the activity index. DETAILED DESCRIPTION

[0019] Calcium silicate hydrate (xCaO•ySiO2•zH2O, C-S-H) nucleating early strength agent is a new type of silicate cement early strength agent, which can provide nucleation sites for the hydration of active minerals in cement, significantly reduce the nucleation potential barrier of hydration products, and greatly accelerate the kinetics of cement hydration reaction, thereby improving the macroscopic performance of cement. Steel slag is rich in calcium components, and its main chemical component is calcium oxide (CaO), which exists in various forms: first, free calcium oxide (f-CaO) with high reactivity; second, dicalcium silicate (C2S) and tricalcium silicate (C3S) in mineral form. Therefore, steel slag has the potential to generate C-S-H as a calcium source. According to the typical pozzolanic reaction mechanism, the dissolution of calcium components in steel slag in alkaline water medium generates Ca 2+ Amorphous or highly active silicon dioxide (SiO2) in the environment can react with C-S-H products. The reason why the siliceous modifier and steel slag can react to generate C-S-H is based on the chemical "calcium-silicon complementary" relationship between the two, through ion dissolution and mass transfer at the interface, and follows the spontaneous pozzolanic reaction principle, which preferentially nucleates on the surface of steel slag under the driving of thermodynamics, and finally realizes the in-situ and efficient synthesis of C-S-H, thereby improving the hydration reactivity of steel slag. The reaction can be spontaneous at normal temperature and pressure, which fundamentally avoids the need for high energy consumption, and the activation cost is greatly reduced compared with traditional mechanical grinding methods.

[0020] Currently commonly used siliceous modifiers mainly include industrial products such as sodium silicate, nano-silicon dioxide or silica sol, etc. Compared with them, using siliceous industrial solid waste as a modifier has a significant strategic advantage in cost. Siliceous tailings are the main type of mine tailings in China (main component is SiO2), which has a research basis for being used as a siliceous modifier. According to the related reports on the synthesis of functional materials from tailings, the alkali medium hydrothermal technology (referred to as "alkali-thermal activation") can significantly improve the leaching rate of active silicon monomers in the tailings. However, the large amount of NaOH consumed in the alkali-thermal activation process greatly increases the cost of tailing 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 tailing activation. Red mud is a typical large amount of solid waste generated by the alumina production industry, which has the characteristics of high alkalinity, fine particle size and complex composition, but its utilization rate is currently low.

[0021] Based on this, the present application provides a method for activating siliceous tailings with red mud as a siliceous modifier to enhance the hydration activity of steel slag, which comprises the following steps: a. Preparing activated tailings; a1. Grinding the red mud and siliceous tailings separately, then mixing them, and then adding NaOH particles and stirring uniformly to obtain a mixed powder; a2, adding deionized water into the mixed powder obtained in step a1 and transferring to a high-speed shearing stirrer for stirring to obtain a mixed paste; adding deionized water into the mixed paste and switching the high-speed shearing stirrer to a magnetic stirring mode for stirring to obtain a first mixed slurry; a3, transferring the first mixed slurry obtained in step a2 to a reaction kettle for reaction; after the reaction is completed, the obtained reaction product is cooled to room temperature, dried and ground into powder to obtain an activated tailings; b, preparing a modified steel slag; b1, mixing the steel slag after grinding with the activated tailings obtained in step a3, adding deionized water, and then transferring to a vortex oscillator for pre-oscillation to obtain a second mixed slurry; b2, transferring the second mixed slurry obtained in step b1 to a constant-temperature oscillation box for oscillation reaction; after the oscillation reaction is completed, centrifugal treatment is performed to obtain a solid product; b3, washing and centrifuging the solid product obtained in step b2 with deionized water to remove residual OH - and Na + , and then drying and grinding into powder to obtain a modified steel slag.

[0022] The present application modifies the steel slag by the activated tailings, generates C-S-H products on the surface of the steel slag, significantly enhances the hydration activity of the steel slag, realizes the resource utilization of red mud, tailings and steel slag, and provides a new idea for the collaborative treatment of multiple solid wastes.

[0023] The present application will be further described below in combination with specific examples. Various chemical reagents used in the examples of the present application are obtained through conventional commercial channels unless otherwise specified.

[0024] In the following examples, the red mud comes from Shandong Aluminum Co., Ltd.; the siliceous tailings come from Shandong Gold Group Penglai Mining Co., Ltd.; the steel slag comes from Qingdao Shenfei Anda Environmental Protection Material Co., Ltd.; and the sand is China ISO standard sand produced by Xiamen Aiseo Standard Sand Co., Ltd.

[0025] Example 1 a, preparation of activated tailings: a1, mixing 20 g of red mud and 70 g of siliceous tailings after grinding respectively, then adding 5 g of NaOH particles and stirring uniformly to obtain a mixed powder; a2, adding 50 g of deionized water into the mixed powder obtained in step a1 and transferring to a high-speed shearing stirrer, stirring at a speed of 10000 rpm for 4 min to obtain a mixed paste; adding 50 g of deionized water into the mixed paste and switching the high-speed shearing stirrer to a magnetic stirring mode, stirring at a speed of 400 rpm for 30 min to obtain a first mixed slurry; a3, the first mixed slurry obtained in step a2 was transferred to a 200 mL hydrothermal reactor, and after sealing, it was reacted at 200°C for 4 h; after the reaction was completed, the obtained reaction product was cooled to room temperature, and then placed in a 100°C vacuum drying oven for drying, and further ground into a powder (less than 74 μm) to obtain the activated tailings.

[0026] b, preparation of modified steel slag: b1, 40 g of steel slag was ground and mixed with 10 g of activated tailings obtained in step a3 and 150 g of deionized water, and then placed in a vortex oscillator for pre-oscillation for 2 min to obtain a second mixed slurry; b2, the second mixed slurry obtained in step b1 was transferred to a constant temperature oscillator for oscillation reaction for 24 h, with the reaction temperature fixed at 25°C and the rotation speed at 180 r / min; after the oscillation reaction was completed, the mixed slurry was subjected to centrifugal treatment by using a centrifuge (rotation speed of 4000 r / min and centrifugal time of 3 min) to obtain a solid product; b3, 150 g of deionized water was added to the solid product obtained in step b2, and then the solid product was re-dispersed in the deionized water by placing it in a vortex oscillator for washing, and the supernatant was discarded after centrifugation, and the above-mentioned “washing-centrifugation” process was repeated until the pH value of the supernatant after washing was stable at 10.0-10.5 and the conductivity was reduced to below 150 μS / cm, which indicated that the impurity ions (OH - and Na + ) had been basically removed; after the washing and centrifugation were completed, the solid product was dried and ground into a powder to obtain the modified steel slag.

[0027] (1) Characterization of activated tailings; In order to characterize the activated tailings, the crystallinity, polymeric structure and leaching rate of active silicon monomers of the activated tailings prepared in Example 1 were analyzed by means of XRD, FTIR and ICP.

[0028] As shown in (a) of FIG. 1, Figure 1 in the XRD spectrum, the diffraction peak intensity of the main mineral phases such as quartz, albite, microcline, mica and the like in the activated tailings was obviously weakened compared with the unactivated tailings, indicating that the crystal structure of the minerals was destroyed, the relative crystallinity was reduced, the amorphous degree was increased, and therefore the reaction activity of the tailings was enhanced.

[0029] As shown in (b) of FIG. 1, Figure 1 in the FTIR spectrum, the absorption peaks near the wave numbers of 3400 cm -1 and 1600 cm -1 were attributed to the bending vibration of -OH and H-O-H bonds in water molecules, and the absorption peaks near the wave numbers of 1440 cm-1 and 1020cm -1 The nearby absorption peaks correspond to the symmetric stretching vibrations of the OCO bonds and the asymmetric stretching vibrations of the Si-O-Si (Al) bonds in the carbonate phase, respectively. Compared with the unactivated tailings, the absorption peak intensities of the bending vibrations of the -OH and HOH bonds in the activated tailings are significantly enhanced, indicating the formation of aqueous activation products in the activated tailings; the enhanced absorption peak intensity of the symmetric stretching vibrations of the OCO bonds indicates that the phases in the tailings underwent a carbonation reaction with CO2 during the alkaline thermal activation process; the wavenumbers of the Si-O-Si (Al) bonds in the activated tailings are significantly lower than those in the unactivated tailings in the FTIR spectrum, indicating that the polymeric structure of the aluminosilicate phase in the tailings decomposes and transforms into a new aluminosilicate phase with a lower degree of polymerization.

[0030] like Figure 1 As shown in (c), the ICP test results indicate that after the activated tailings are contacted with the aqueous solution, the activated Si... 4+ The leaching rate was significantly increased to 4764 mg / L, which indicates that activated tailings can be used as a silica modifier to enhance the hydration activity of steel slag.

[0031] The results of XRD, FTIR, and ICP tests indicate that during the alkaline thermal activation process using red mud as the main alkali source and supplemented with a small amount of NaOH, the stable crystal structure of the tailings is disrupted. The main mineral phases in the tailings, such as quartz, albite, microcline, and mica, are transformed into activated aluminosilicate products with a lower degree of polymerization. These activated products are readily soluble in water and can release a large amount of active Si. 4+ .

[0032] (2) Characterization of the modified steel slag; To characterize the modified steel slag, the phase composition, polymer structure, microstructure and pore size distribution of the modified steel slag prepared in Example 1 were analyzed using XRD, FTIR, SEM and BET methods, revealing the modification mechanism of activated tailings as a siliceous modifier on steel slag.

[0033] like Figure 2 As shown in (a), in the XRD pattern, compared with the unmodified steel slag, the diffraction peak intensities of dicalcium ferrite, calcium aluminate, tricalcium silicate, and dicalcium silicate in the modified steel slag are all reduced, indicating that these active phases reacted during the modification process of the steel slag. Figure 2 As shown in (b), comparing the FTIR spectra of steel slag before and after modification, the most obvious change is that the wavenumber of the asymmetric stretching vibration peak of the Si-O-Si (Al) bond in the modified steel slag is significantly higher than that in the unmodified steel slag. This is likely because the modified steel slag produces CSH products with a higher degree of polymerization.

[0034] likeFigure 3 As shown in (a), the surface of the unmodified steel slag particles is relatively smooth in the SEM image, making it difficult to observe the presence of micropores; further EDS analysis of the unmodified steel slag particles in Region A shows... Figure 3 As shown in (a), the most abundant element is Ca, which is consistent with the characteristic of steel slag being rich in calcium components. Figure 3 As shown in (b), in the SEM image, the surface of the modified steel slag is rougher than that of the unmodified steel slag, with a large number of network-like products covering the surface of the steel slag particles, and numerous pores can be observed; further EDS analysis of the network-like products, such as... Figure 3 As shown in (b), the product is rich in Ca, Si and O, which proves that the product is a CSH product.

[0035] like Figure 4 As shown in Figures (a) and (b), the pore size distribution curves and cumulative pore volume curves clearly demonstrate that the porosity of the steel slag significantly increases after modification with the activated tailings silica modifier. This is mainly related to the formation of network-like, porous CSH products. Further referring to Table 1, it can be seen that compared to the unmodified steel slag, the average pore size of the modified steel slag decreases to 16.1484 nm, and the cumulative pore volume increases to 0.09458 cm³. 3 / g, while the specific surface area increased significantly to 19.3127 cm². 2 / g, approximately 10 times that of unmodified steel slag. These results indicate that, under aqueous conditions, activated tailings, acting as a siliceous modifier, can effectively release active silicon monomers and react with the calcium components in the steel slag in a pozzolanic reaction. This generates a large number of network-like, porous CSH products on the surface of the steel slag particles, significantly increasing the specific surface area of ​​the steel slag and thus achieving the purpose of modifying it.

[0036] The abbreviations above are explained as follows: FTIR: Fourier Transform Infrared Spectroscopy; XRD: X-ray Diffraction Pattern; ICP: Inductively Coupled Plasma Spectroscopy; SEM: Scanning Electron Microscopy; EDS: Energy Dispersive X-ray Spectroscopy; BET: Surface Area Measurement Technique.

[0037] Table 1 Key pore structure parameters of steel slag before and after modification (3) The evolution of the activity index of steel slag before and after modification; The following scheme illustrates the evolution of the activity index of steel slag before and after modification, wherein the modified steel slag used is the modified steel slag prepared in Example 1.

[0038] The experiment further determines the hydration activity index of the modified steel slag according to the technical specification of GB 2847-2005 “pozzolanic materials for use in cement”. The control group and the experimental group are set. The control group is a mortar sample prepared from 30% unmodified steel slag + 70% Portland cement, and the experimental group is a mortar sample prepared from 30% modified steel slag + 70% Portland cement. The mortar is stirred uniformly in a mortar mixer according to the water-cement ratio of 0.5 and the cement-sand ratio of 1:3. The mixed slurry is poured into a 4x4x16 cm stainless steel mold, and is cured in a standard constant temperature and humidity curing box (temperature 20 ℃, relative humidity ≥ 90%). The compressive strength of the mortar sample (including the control group and the experimental group) is determined at 3, 7 and 28 days of curing age, respectively, and is compared with the compressive strength of the 42.5 Portland cement mortar sample (without adding steel slag, material ratio: water-cement ratio of 0.5, cement-sand ratio of 1:3) to determine the activity level.

[0039] As shown in Figure 5 , the compressive strength and activity index of the experimental group are higher than those of the control group throughout the curing age; as shown in Figure 5 (a) (the red dotted lines respectively represent the compressive strength of the 42.5 Portland cement mortar sample cured for 3 days, 7 days and 28 days), the compressive strength of the control group at 3 days, 7 days and 28 days is 11.61 MPa, 18.31 MPa and 32.31 MPa, respectively, which is much lower than the compressive strength of the 42.5 Portland cement mortar sample at the same age (3 days: 23.35 MPa; 7 days: 31.21 MPa; 28 days: 45.28 MPa), and the corresponding 3-day, 7-day and 28-day activity indexes are only 49.72%, 58.67% and 71.36%, respectively, indicating that the hydration activity of the unmodified steel slag is low. Compared with the control group, the compressive strength of the experimental group at 3 days, 7 days and 28 days reaches 18.95 MPa, 28.91 MPa and 45.56 MPa, respectively, and the compressive strength is significantly enhanced, and the 28-day compressive strength is even slightly higher than that of the 42.5 Portland cement mortar sample; the activity indexes of the modified steel slag at 3 days, 7 days and 28 days are 81.16%, 92.63% and 100.62%, respectively, which are significantly higher than those of the unmodified steel slag, and the 28-day activity index is much higher than the requirement of GB 2847-2005 “pozzolanic materials for use in cement” (65%). The improvement of the activity index of the modified steel slag is closely related to the nucleation effect of C-S-H, which is generated on the surface of the steel slag particles, is loose and porous, has a large specific surface area, can provide nucleation sites for cement hydration, reduce the nucleation potential barrier of the hydration products, and accelerate the hydration process of cement, thereby enhancing the hydration activity of the steel slag. The above results show that the red mud activated tailings as a siliceous modifier can effectively enhance the hydration activity of the steel slag, and greatly improve the application potential of the steel slag in the field of building materials.

[0040] On the basis of the above-mentioned embodiments, the application further has the following embodiments.

[0041] Embodiment 2 a. Preparation of activated tailings: a1. 18 g of red mud and 65 g of siliceous tailings were respectively ground and mixed, then 4 g of NaOH particles were added and stirred uniformly to obtain a mixed powder; a2. 45 g of deionized water was added to the mixed powder obtained in step a1 and transferred to a high-speed shearing stirrer, and stirred at a speed of 10000 rpm for 4 min to obtain a mixed paste; 45 g of deionized water was further added to the mixed paste, and the high-speed shearing stirrer was switched to a magnetic stirring mode, and stirred at a speed of 400 rpm for 30 min to obtain a first mixed slurry; a3. The first mixed slurry obtained in step a2 was transferred to a 200 mL hydrothermal reaction kettle, sealed and reacted at 190℃ for 4.5 h; after the reaction was completed, the obtained reaction product was cooled to room temperature, then placed in a 100℃ vacuum drying oven for drying, and further ground into powder (less than 74 μm) to obtain activated tailings.

[0042] b. Preparation of modified steel slag: b1. 35 g of steel slag was ground and mixed with 8 g of activated tailings obtained in step a3 and 140 g of deionized water, then placed in a vortex shaker for pre-oscillation for 2 min to obtain a second mixed slurry; b2. The second mixed slurry obtained in step b1 was transferred to a constant-temperature oscillation box and oscillated for 24 h, the reaction temperature was fixed at 25℃, and the rotation speed was 180 r / min; after the oscillation reaction was completed, the mixed slurry was centrifuged by a centrifuge (at a speed of 4000 r / min for 3 min) to obtain a solid product; b3. 140 g of deionized water was added to the solid product obtained in step b2, then the solid product was dispersed in the deionized water again in a vortex shaker for washing, and the supernatant was discarded after centrifugation, and the above-mentioned “washing-centrifugation” process was repeated until the pH value of the supernatant after washing was stable at 10.0-10.5 and the conductivity was reduced to below 150 μS / cm, which indicated that the impurity ions (OH - and Na + ) had been basically removed; after the washing and centrifugation were completed, the solid product was dried and ground into powder to obtain modified steel slag.

[0043] Embodiment 3 a. Preparation of activated tailings: a1, 22 g of red mud and 75 g of siliceous tailings were ground respectively and mixed, then 6 g of NaOH particles were added and stirred uniformly to obtain a mixed powder; a2, 55 g of deionized water was added to the mixed powder obtained in step a1 and transferred to a high-speed shearing stirrer, stirred at 10000 rpm for 4 min to obtain a mixed paste; 55 g of deionized water was further added to the mixed paste, and the high-speed shearing stirrer was switched to a magnetic stirring mode, stirred at 400 rpm for 30 min to obtain a first mixed slurry; a3, the first mixed slurry obtained in step a2 was transferred to a 200 mL hydrothermal reactor, sealed and reacted at 210°C for 3.5 h; after the reaction was completed, the obtained reaction product was cooled to room temperature, then placed in a 100°C vacuum drying oven for drying, and further ground into powder (less than 74 μm) to obtain an activated tailings.

[0044] b, preparation of modified steel slag: b1, 45 g of steel slag was ground and mixed with 12 g of activated tailings obtained in step a3 and 160 g of deionized water, then placed in a vortex shaker for 2 min of pre-vibration to obtain a second mixed slurry; b2, the second mixed slurry obtained in step b1 was transferred to a constant temperature oscillation box and oscillated for 24 h, the reaction temperature was fixed at 25°C, and the rotation speed was 180 r / min; after the oscillation reaction was completed, the mixed slurry was centrifuged by a centrifuge (rotation speed of 4000 r / min, centrifugation time of 3 min) to obtain a solid product; b3, 160 g of deionized water was added to the solid product obtained in step b2, then the solid product was dispersed in deionized water in a vortex shaker for washing, and the supernatant was discarded by centrifugation, and the above-mentioned “washing-centrifugation” process was repeated until the pH value of the supernatant after washing was stable at 10.0-10.5 and the conductivity was reduced to below 150 μS / cm, which indicated that the impurity ions (OH - and Na + ) had been basically removed; after the washing and centrifugation were completed, the solid product was dried and ground into powder to obtain a modified steel slag.

[0045] The parts not mentioned in the above embodiments can be realized or referred to the existing technology.

[0046] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above-mentioned embodiments, and the changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should be within the scope of the present application.

Claims

1. A method for using red mud-activated siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag, characterized in that, Includes the following steps: a. Preparation of activated tailings; a1. Grind the red mud and siliceous tailings separately and then mix them together. Then add NaOH particles and stir evenly to obtain a mixed powder. a2. Add deionized water to the mixed powder obtained in step a1 and transfer it to a high-speed shear mixer for stirring to obtain a mixed paste; add deionized water to the mixed paste again, switch the high-speed shear mixer to magnetic stirring mode for stirring to obtain the first mixed slurry; a3. Transfer the first mixed slurry obtained in step a2 to a reactor for reaction; after the reaction is completed, cool the obtained reactants to room temperature, dry and grind them into powder to obtain activated tailings; b. Preparation of modified steel slag; b1. Grind the steel slag and mix it with the activated tailings obtained in step a3. Add deionized water and then transfer it to a vortex shaker for pre-vibration to obtain a second mixed slurry. b2. Transfer the second mixed slurry obtained in step b1 to a constant temperature shaking chamber for shaking reaction; after the shaking reaction is completed, centrifuge to obtain solid product; b3. Wash and centrifuge the solid product obtained in step b2 with deionized water to remove residual OH-. - and Na + The slag is then dried and ground into powder to obtain modified steel slag.

2. The method for using red mud-activated siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag according to claim 1, characterized in that, In step a: the ratio of red mud, NaOH, siliceous tailings and deionized water is 18-22 g: 4-6 g: 65-75 g: 90-110 g.

3. The method for using red mud-activated siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag according to claim 1, characterized in that, Step a2 specifically includes the following steps: adding deionized water to the mixed powder obtained in step a1 and transferring it to a high-speed shear mixer for stirring at a stirring rate of 8000-12000 rpm for 3-5 min to obtain a mixed paste; adding deionized water to the mixed paste and switching the high-speed shear mixer to magnetic stirring mode for stirring at a stirring rate of 300-500 rpm for 25-35 min to obtain a first mixed slurry.

4. The method for using activated red mud siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag according to claim 1, characterized in that, In step a3: the reaction temperature is 190-210 ℃ and the time is 3.5-4.5 h; the drying temperature is 90-110 ℃ and the particle size of the powder is less than 74 μm.

5. The method for using red mud-activated siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag according to claim 1, characterized in that, In step b1: the ratio of activated tailings, steel slag and deionized water is 8-12 g: 35-45 g: 140-160 g.

6. The method for using red mud-activated siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag according to claim 1, characterized in that, In step b1: the pre-oscillation time is 2-3 minutes.

7. The method for using red mud-activated siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag according to claim 1, characterized in that, In step b2: the reaction temperature of the constant temperature shaking chamber is set to 20-30 ℃, the rotation speed is 170-190 r / min, and the reaction time is 23-25 ​​h; the centrifugation speed is 3500-4500 r / min, and the time is 2-4 min.

8. The method for using red mud-activated siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag according to claim 1, characterized in that, In step b3: the pH value of the supernatant after washing is 10.0-10.5, and the conductivity is less than 150 μS / cm; the drying temperature is 45-55 ℃, and the particle size range of the powder is less than 74 μm.

9. The method for using activated red mud siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag according to claim 1, characterized in that, The chemical composition of the red mud, by mass percentage, includes: Fe2O3 32-38%, Al2O3 18-20%, SiO2 15-17%, Na2O 7-9%; the chemical composition of the siliceous tailings includes: SiO2 70-75%, Al2O3 12-15%, Na2O 3-4%, K2O 4-6%; and the chemical composition of the steel slag includes: CaO 43-47%, SiO2 20-23%, Al2O3 5-7%, Fe2O3 15-18%.

10. The method for using red mud-activated siliceous tailings as a siliceous modifier to enhance the hydration activity of steel slag according to claim 1, characterized in that, The modified steel slag obtained by this method was mixed with 42.5 silicate cement at a mass ratio of 3:7, and stirred evenly in a mortar mixer at a water-cement ratio of 0.5 and a cement-sand ratio of 1:3 to obtain a mixed slurry. The compressive strength of the mixed slurry after curing for 3 days, 7 days and 28 days reached 18.95 MPa, 28.91 MPa and 45.56 MPa, respectively, and the corresponding activity indices reached 81.16%, 92.63% and 100.62%, respectively.

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