A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste

Abstract

This invention belongs to the field of inorganic non-metallic materials technology, and specifically relates to a low-carbon, high-iron sulfoaluminate cementitious material based on steel slag solid waste. It comprises the following raw materials in parts by weight: limestone 35-55 parts, anhydrite 10-20 parts, bauxite 20-45 parts, modified steel slag A 8-15 parts, and modified steel slag B 5-10 parts. Modified steel slag A is activated by acid / alkali, doped with calcium fluoride / sodium sulfate / titanium dioxide and calcined, and then in-situ co-precipitated to introduce magnesium aluminum spinel nanocrystals. This is used for raw material calcination, which can reduce the calcination temperature, refine the clinker grains, and improve early strength. Modified steel slag B is activated by acid / alkali, doped and calcined, and coated with silane coupling agent / polyvinyl alcohol / silica ball milling. It is incorporated as a blending material to improve the interface, slow-release hydration, and improve later-stage strength. This invention achieves high-value utilization of steel slag through synergistic modification, and the cementitious material has advantages such as low carbon content, early and high strength, suitable setting time, and excellent stability.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials technology, specifically to a low-carbon, high-iron sulfoaluminate cementitious material based on steel slag solid waste. Background Technology

[0002] Sulfoaluminate cement, with its excellent properties such as early strength, high strength, frost resistance, impermeability, and corrosion resistance, is widely used in special engineering fields. High-speed ferroaluminate cement, in particular, has further optimized iron phase composition, exhibiting superior resistance to sulfate attack, making it especially suitable for harsh environments such as marine engineering. However, the production of traditional sulfoaluminate cement still mainly relies on natural limestone, bauxite, gypsum, and other mineral resources, resulting in high resource consumption and carbon emissions. On the other hand, steel slag, a major industrial solid waste generated during steelmaking, has an annual production of nearly 100 million tons in my country. Its comprehensive utilization rate is low, and large-scale stockpiling not only occupies land resources but also causes environmental problems such as soil and water pollution. Steel slag contains abundant CaO, Fe2O3, Al2O3, and other components, possessing the potential to replace some cement raw materials. However, the direct use of steel slag in building materials faces technical bottlenecks such as poor volume stability due to free calcium oxide (f-CaO) and free magnesium oxide (f-MgO), high metallic iron content, and large compositional fluctuations, limiting its large-scale application in the cement industry.

[0003] Patent application CN201910300484.4 discloses a method and system for producing low-alkalinity, novel mineral-based sulfoaluminate cement using steel slag. The method involves mixing ground steel slag with desulfurized gypsum, alumina ash, and carbide slag in a predetermined ratio, followed by direct calcination at 1200-1270℃ to obtain cement clinker. This method overcomes the traditional requirements for calcium, aluminum, and iron content in sulfoaluminate cement production, enabling the large-scale application of solid waste steel slag. However, in this technical solution, the steel slag is directly fed into the kiln without any pretreatment. The f-CaO and f-MgO in the steel slag are not effectively eliminated, and the residual free oxides in the clinker easily lead to poor cement stability. Simultaneously, the cementitious activity of the steel slag is not fully activated, and the cement strength decreases significantly with increasing admixture dosage, limiting the further high-value utilization of steel slag. Patent application CN201510010803.X discloses an aluminate cement containing nano-magnesium aluminum spinel and its preparation method. This invention uses natural dolomite and industrial alumina as raw materials to synthesize aluminate cement containing magnesium aluminum spinel at 1000-1600℃. However, the particle size of the magnesium aluminum spinel in this method is in the micrometer range and cannot be effectively controlled, resulting in limited seed crystal refinement of the clinker minerals. The steel slag phase-separated clinker calcination technology involves feeding steel slag into the rising flue between the kiln tail and the decomposition furnace. During calcination, fine-particle steel slag acts as a seed crystal, promotes melting, and granulates. However, in this technology, the seed crystal function of the steel slag is passively activated rather than actively introducing highly active nano-seed crystals, and the grain refinement effect is limited by the particle size and composition of the steel slag itself.

[0004] Therefore, how to prepare a cementitious material with advantages such as low carbon content, early and high strength, suitable setting time, and excellent stability while ensuring the efficient, stable, and high-value utilization of steel slag has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a low-carbon, high-ferrous sulfoaluminate cementitious material based on steel slag solid waste. The process involves three steps: sequential acid / alkali composite activation, ion doping at high temperature, and in-situ co-precipitation crystallization to obtain modified steel slag A with magnesium-aluminum spinel nanocrystals on its surface. Simultaneously, the ion-doped steel slag is mechanically and chemically coated with a silane coupling agent / polyvinyl alcohol / nano silica to obtain modified steel slag B. Modified steel slag A is then used as a raw material component in a kiln with limestone, anhydrite, and bauxite for low-temperature calcination. Modified steel slag B is used as a blending material and co-ground with clinker. This results in a low-carbon, high-ferrous sulfoaluminate cementitious material with early strength, high strength, stable volume, reasonable setting time, and low water consumption.

[0006] The technical solution of the present invention to solve the above problems is as follows: A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste comprises the following raw materials in parts by weight: 35-55 parts limestone, 10-20 parts anhydrite, 20-45 parts bauxite, 8-15 parts modified steel slag A, and 5-10 parts modified steel slag B. The modified steel slag A is prepared as follows: Step S1: Crush the steel slag, remove iron, then add phosphoric acid solution, react at 50-60℃ for 50-70 minutes, filter after the reaction, add sodium hydroxide solution to the filter cake, react at 70-80℃ for 30-50 minutes, and obtain activated steel slag after post-treatment after the reaction. Step S2: Add calcium fluoride, sodium sulfate and titanium dioxide to activated steel slag and mix for 30-40 min. Then, under inert gas protection, heat to 690-710℃ and hold for 110-130 min. Then cool to room temperature to obtain doped steel slag. Step S3: Add the composite salt solution to the doped steel slag and start stirring. Heat to 75-85℃, adjust the pH to 9.5-10.5, and then continue stirring for 1-2 hours. After the reaction is completed, post-treatment is performed to obtain modified steel slag A.

[0007] Further, in step S1, the mass ratio of phosphoric acid solution to steel slag is 2.5-3.5:1, the concentration of phosphoric acid solution is 9.5-10.5 wt%, the mass ratio of sodium hydroxide solution to filter cake is 2-3:1, and the concentration of sodium hydroxide solution is 7.5-8.5 wt%.

[0008] Further, the mass ratio of calcium fluoride, sodium sulfate, titanium dioxide, and activated steel slag in step S2 is 0.015-0.025:0.005-0.015:0.003-0.007:1.

[0009] Further, the composite salt solution mentioned in step S3 is a mixed aqueous solution of magnesium nitrate, aluminum nitrate, and calcium nitrate, with the mass ratio of magnesium nitrate, aluminum nitrate, calcium nitrate, and doped steel slag being 2.5-3.5:7-8:0.5-1.5:100, and the concentration of magnesium nitrate in the composite salt solution being 40-60 g / L.

[0010] Furthermore, the modified steel slag B is prepared as follows: silane coupling agent KH-550, polyvinyl alcohol, and silicon dioxide are added to the doped steel slag obtained in step S2, ball-milled for 30-60 minutes, and then sieved to obtain modified steel slag B.

[0011] Furthermore, the mass ratio of the silane coupling agent KH-550, polyvinyl alcohol, silicon dioxide, and the doped steel slag obtained in step S2 is 1.5-3:0.5-1:2-5:100.

[0012] Furthermore, the aforementioned low-carbon high-ferrous sulfoaluminate cementitious material based on steel slag solid waste is prepared by the following method: Step (1) grind limestone, bauxite and anhydrite separately until the residue on an 80μm square hole sieve is ≤10%, and then mix them with modified steel slag A to obtain raw material; Step (2) involves preheating, decomposing, and calcining the raw materials in sequence, followed by cooling, and then discharging the cooked materials to obtain the clinker. Step (3) Grind the clinker to a specific surface area of ​​330-360 m2 / kg, add modified steel slag B and dihydrate gypsum, and grind them together to a specific surface area of ​​420-460 m2 / kg to obtain the final product.

[0013] Furthermore, the preheating, decomposition, and firing temperatures in step (2) are 790-810℃, 1090-1110℃, and 1240-1260℃, respectively.

[0014] Furthermore, the mass ratio of dihydrate gypsum to clinker in step (3) is 0.03-0.08:1.

[0015] The present invention has the following beneficial effects: This invention first modifies steel slag in two separate ways to prepare modified steel slag A and modified steel slag B, which are then synergistically applied to a low-carbon, high-iron sulfoaluminate cementitious material system. Modified steel slag A undergoes a three-step treatment: acid / alkali composite activation, ion-doped nucleation induction, and in-situ co-precipitation-crystallization. This process forms calcium fluoride, calcium titanate microcrystals, and magnesium aluminum spinel nanocrystals on the slag surface. These seeds act as highly efficient mineralizers and heterogeneous nucleating agents during clinker firing, significantly lowering the liquidus appearance temperature and promoting the low-temperature formation of anhydrous calcium sulfoaluminate and tetracalcium aluminoferrite at 1240-1260℃. This results in a significant increase in the early-stage (3d, 7d) compressive and flexural strength of the cementitious material, a slight shortening of the setting time, and a reduction in the standard consistency water requirement. Simultaneously, free calcium oxide and free magnesium oxide in modified steel slag A are eliminated, ensuring satisfactory stability. Modified steel slag B, after acid / alkali activation, ion doping, and mechanochemical organic-inorganic composite coating, retains an active silica-alumina layer, calcium fluoride / calcium titanate microcrystals, and a silane coupling agent-polyvinyl alcohol-nano silica coating film on its surface. When incorporated into the mixture during grinding, its organic-inorganic composite coating improves particle dispersibility and interfacial compatibility, optimizes the later hydration process through a slow-release effect, and generates an interfacial reinforcement effect with the clinker matrix formed by modified steel slag A, further enhancing the slurry density and long-term strength stability (28-day compressive and flexural strength).

[0016] Limestone, anhydrite, bauxite, and modified steel slag A together constitute the raw meal, which is calcined into clinker at 1240-1260℃. The calcium fluoride, calcium titanate, and magnesium aluminum spinel seed crystals provided by the modified steel slag A undergo a synergistic mineralization reaction with the calcium, silicon, aluminum, sulfur, iron, and other components in the limestone, bauxite, and anhydrite. This not only reduces calcination energy consumption but also makes the clinker mineral grains more uniform and refined, thus endowing the clinker with excellent hydration activity. At the same time, the active silica-alumina layer generated by acid / alkali activation in the modified steel slag A promotes the uniformity of solid-phase reaction during calcination, further optimizing the mineral composition of the clinker. After calcination, the clinker is ground and then ground together with modified steel slag B and dihydrate gypsum to the specified fineness. At this time, the active silica-alumina layer, calcium fluoride / calcium titanate microcrystals, and organic-inorganic composite coating in modified steel slag B have a synergistic effect with the clinker particles and gypsum: on the one hand, the microcrystals in modified steel slag B induce the uniform precipitation of clinker mineral hydration products, making the cement stone structure more compact; on the other hand, the nano silica in the coating slowly releases silicon ions in the alkaline environment, which react with the calcium hydroxide produced by cement hydration to generate additional hydrated calcium silicate, while the silane coupling agent strengthens the interfacial bonding between the steel slag particles and the cement paste through chemical bonding. The above-mentioned components are interdependent and indispensable in terms of raw material ratio, seed crystal introduction, firing regime, and grinding process. Therefore, this invention achieves high-value utilization of steel slag through the synergistic combination of modified steel slag and basic raw materials, significantly improving the standard consistency water consumption, setting time, stability, flexural and compressive strength at various ages of cementitious materials, and achieving unexpected technical effects that cannot be achieved by a single component or simple combination. Attached Figure Description

[0017] Figure 1 The results of the water content test for standard consistency of cement; Figure 2 These are the test results for compressive strength and flexural strength at different ages. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] All raw materials used in the following examples are commercially available products. Limestone with an effective component content of 97% and a moisture content of ≤0.01% was sourced from Lingshou County Defa Mineral Products Processing Plant; bauxite with an Fe2O3 content of 2% and a particle size of 325μm was sourced from Shijiazhuang Hualang Mineral Products Trading Co., Ltd.; anhydrite, model 564, was sourced from Zaozhuang Xinghao New Materials Co., Ltd.; steel slag, with a specification of 20-40 mesh and a moisture content of ≤3.0%, was sourced from Tianjin Hongqiao District Tianbao Haotong Stone Processing Plant; polyvinyl alcohol, model 0588, with an effective component content of 99%, was sourced from Jining Fangyu Chemical Co., Ltd.; silica, with an effective component content of 99% and a particle size of 15nm, was sourced from Lvlian (Jining) Chemical Technology Co., Ltd.; and dihydrate gypsum was purchased from Shandong Longbang Gypsum Products Co., Ltd.

[0020] Example 1 A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste comprises the following raw materials in parts by weight: 35 parts limestone, 10 parts anhydrite, 20 parts bauxite, 8 parts modified steel slag A, and 5 parts modified steel slag B. The modified steel slag A is prepared as follows: Step S1: The steel slag is crushed to ≤10mm using a jaw crusher, and iron is removed by an electromagnetic separator with a magnetic field strength ≥0.3T. Then, phosphoric acid solution is added, and the mixture is reacted at 55℃ for 60 minutes. After the reaction, the mixture is filtered, and sodium hydroxide solution is added to the filter cake. The mixture is reacted at 75℃ for 40 minutes, and after the reaction, it is filtered again. The filter cake is washed with deionized water until the pH reaches 7-8. The filter cake is then dried in a 110℃ hot air drying oven for 2 hours to obtain activated steel slag. The mass ratio of phosphoric acid solution to steel slag is 3:1, and the concentration of phosphoric acid solution is 10wt%. The mass ratio of sodium hydroxide solution to filter cake is 2.5:1, and the concentration of sodium hydroxide solution is 8wt%. Step S2: Add calcium fluoride, sodium sulfate, and titanium dioxide to the activated steel slag and mix for 35 min. Then, under nitrogen protection, heat the mixture to 700℃ at 10℃ / min and hold for 120 min. Finally, cool the mixture rapidly to room temperature at a rate of 20℃ / min to obtain doped steel slag. The mass ratio of calcium fluoride, sodium sulfate, titanium dioxide, and activated steel slag is 0.02:0.01:0.005:1. Step S3: Add the composite salt solution to the doped steel slag and start stirring at 150 rpm. Heat to 80°C and add 10% ammonia solution to adjust the pH to 9.5-10.5 at a rate of 0.3 L / min. Continue stirring for 1.5 h. After the reaction is complete, filter and wash the filter cake with deionized water until the pH is 8. Then dry in a hot air drying oven at 110°C for 3 h. Then heat the dried steel slag to 850°C in air at a rate of 10°C / min and hold for 2 h. Finally, rapidly cool to room temperature at a rate of 40°C / min to obtain modified steel slag A. The composite salt solution is a mixed aqueous solution of magnesium nitrate, aluminum nitrate, and calcium nitrate. The mass ratio of magnesium nitrate, aluminum nitrate, calcium nitrate, and doped steel slag is 3:7.5:1:100, and the concentration of magnesium nitrate in the composite salt solution is 50 g / L.

[0021] The modified steel slag B is prepared as follows: Silane coupling agent KH-550, polyvinyl alcohol, and silicon dioxide are added to the doped steel slag obtained in step S2, and ball-milled for 45 minutes at a speed of 300 rpm with a ball-to-material ratio of 5:1. Zirconia balls are selected, with large, medium, and small ball diameters of 20 mm, 15 mm, and 10 mm, respectively, and a mass ratio of large, medium, and small balls of 2:3:5. Then, the modified steel slag B is obtained by passing it through a 100-mesh sieve, wherein the mass ratio of silane coupling agent KH-550, polyvinyl alcohol, silicon dioxide, and the doped steel slag obtained in step S2 is 2:0.8:3:100.

[0022] The aforementioned low-carbon, high-ferric sulfoaluminate cementitious material based on steel slag solid waste is prepared by the following method: Step (1) Grind limestone, bauxite and anhydrite separately until the residue on an 80μm square hole sieve is ≤10%, and then mix them evenly with modified steel slag A to obtain raw material; Step (2) The raw material is preheated, decomposed, and calcined in sequence, and then cooled to obtain clinker. The cooling wind speed is 2.5 m / s, the cooling rate is 28℃ / s, the discharge temperature is ≤100℃, and the preheating, decomposition, and calcination temperatures are 790℃, 1090℃, and 1240℃, respectively. Step (3) Grind the clinker to a specific surface area of ​​330-360 m². 2 / kg, add modified steel slag B and dihydrate gypsum, and grind together to a specific surface area of ​​420-460m². 2 / kg, which gives the mass ratio of dihydrate gypsum to clinker of 0.03:1.

[0023] Example 2 A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste comprises the following raw materials in parts by weight: 55 parts limestone, 20 parts anhydrite, 45 parts bauxite, 15 parts modified steel slag A, and 10 parts modified steel slag B. The preparation methods of modified steel slag A and modified steel slag B are the same as in Example 1.

[0024] In the above-mentioned preparation method of low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste, the preheating, decomposition and firing temperatures are 810℃, 1110℃ and 1260℃ respectively, the mass ratio of dihydrate gypsum to clinker is 0.08:1, and the rest is the same as in Example 1.

[0025] Example 3 A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste comprises the following raw materials in parts by weight: 45 parts limestone, 15 parts anhydrite, 35 parts bauxite, 10 parts modified steel slag A, and 8 parts modified steel slag B. The preparation methods of modified steel slag A and modified steel slag B are the same as in Example 1.

[0026] In the above-mentioned preparation method of low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste, the preheating, decomposition and firing temperatures are 800℃, 1100℃ and 1250℃ respectively, the mass ratio of dihydrate gypsum to clinker is 0.05:1, and the rest is the same as in Example 1.

[0027] Example 4 A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste comprises the following raw materials in parts by weight: 35 parts limestone, 10 parts anhydrite, 20 parts bauxite, 8 parts modified steel slag A, and 5 parts modified steel slag B. The modified steel slag A is prepared as follows: Step S1: The steel slag is crushed to ≤10mm using a jaw crusher, and iron is removed by an electromagnetic separator with a magnetic field strength ≥0.3T. Then, phosphoric acid solution is added, and the mixture is reacted at 60℃ for 70 minutes. After the reaction, the mixture is filtered, and sodium hydroxide solution is added to the filter cake. The mixture is reacted at 80℃ for 50 minutes, and after the reaction, it is filtered again. The filter cake is washed with deionized water until the pH reaches 7-8. The filter cake is then dried in a hot air drying oven at 110℃ for 2 hours to obtain activated steel slag. The mass ratio of phosphoric acid solution to steel slag is 3.5:1, and the concentration of phosphoric acid solution is 10.5wt%. The mass ratio of sodium hydroxide solution to filter cake is 3:1, and the concentration of sodium hydroxide solution is 8.5wt%. Step S2: Add calcium fluoride, sodium sulfate, and titanium dioxide to the activated steel slag and mix for 40 min. Then, under nitrogen protection, heat the mixture to 710°C at 10°C / min and hold for 130 min. Finally, rapidly cool the mixture to room temperature at a rate of 20°C / min to obtain the doped steel slag. The mass ratio of calcium fluoride, sodium sulfate, titanium dioxide, and activated steel slag is 0.025:0.015:0.007:1. Step S3: Add the composite salt solution to the doped steel slag and start stirring at 150 rpm. Heat to 85°C and add 10% ammonia solution dropwise to adjust the pH to 9.5-10.5 at a rate of 0.3 L / min. Continue stirring for 2 hours. After the reaction is complete, filter the slag. Wash the filter cake with deionized water until the pH reaches 8. Then dry it in a hot air drying oven at 110°C for 3 hours. Then heat the dried steel slag to 850°C in air at a rate of 10°C / min and hold for 2 hours. Finally, rapidly cool it to room temperature at a rate of 40°C / min to obtain modified steel slag A. The composite salt solution is a mixed aqueous solution of magnesium nitrate, aluminum nitrate, and calcium nitrate. The mass ratio of magnesium nitrate, aluminum nitrate, calcium nitrate, and doped steel slag is 3.5:8:1.5:100. The concentration of magnesium nitrate in the composite salt solution is 60 g / L.

[0028] The modified steel slag B is prepared as follows: Silane coupling agent KH-550, polyvinyl alcohol, and silicon dioxide are added to the doped steel slag obtained in step S2, and ball-milled for 60 minutes at a speed of 300 rpm with a ball-to-material ratio of 5:1. Zirconia balls are selected, with large, medium, and small ball diameters of 20 mm, 15 mm, and 10 mm, respectively, and a mass ratio of large, medium, and small balls of 2:3:5. Then, the modified steel slag B is obtained by passing it through a 100-mesh sieve, wherein the mass ratio of silane coupling agent KH-550, polyvinyl alcohol, silicon dioxide, and the doped steel slag obtained in step S2 is 3:1:5:100.

[0029] In the above-mentioned preparation method of low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste, the preheating, decomposition and firing temperatures are 800℃, 1100℃ and 1250℃ respectively, the mass ratio of dihydrate gypsum to clinker is 0.05:1, and the rest is the same as in Example 1.

[0030] Comparative Example 1 A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste comprises the following raw materials in parts by weight: 35 parts limestone, 10 parts anhydrite, 20 parts bauxite, 5 parts modified steel slag A, and 15 parts modified steel slag B. The modified steel slag A is prepared as follows: Step S1: The steel slag is crushed to ≤10mm using a jaw crusher, and iron is removed by an electromagnetic separator with a magnetic field strength ≥0.3T. Then, phosphoric acid solution is added, and the mixture is reacted at 60℃ for 70min. After the reaction, the mixture is filtered, and sodium hydroxide solution is added to the filter cake. The mixture is reacted at room temperature for 50min, and after the reaction, it is filtered again. The filter cake is washed with deionized water until the pH reaches 7-8. The filter cake is then dried in a 110℃ hot air drying oven for 2h to obtain activated steel slag. The mass ratio of phosphoric acid solution to steel slag is 1:1, and the concentration of phosphoric acid solution is 10.5wt%. The mass ratio of sodium hydroxide solution to filter cake is 3:1, and the concentration of sodium hydroxide solution is 1wt%. Step S2: Add calcium fluoride, sodium sulfate, and titanium dioxide to the activated steel slag and mix for 40 min. Then, heat the mixture to 710℃ at a rate of 10℃ / min and hold for 130 min. Finally, rapidly cool the mixture to room temperature at a rate of 20℃ / min to obtain doped steel slag. The mass ratio of calcium fluoride, sodium sulfate, titanium dioxide, and activated steel slag is 0.025:0.001:0.007:1. Step S3: Add the composite salt solution to the doped steel slag and start stirring at 150 rpm. Heat to 85°C and add 10% ammonia solution dropwise to adjust the pH to 9.5-10.5 at a rate of 0.3 L / min. Continue stirring for 2 hours. After the reaction is complete, filter the slag. Wash the filter cake with deionized water until the pH reaches 8. Then dry it in a hot air drying oven at 110°C for 3 hours. Then heat the dried steel slag to 850°C in air at a rate of 10°C / min and hold for 2 hours. Finally, rapidly cool it to room temperature at a rate of 40°C / min to obtain modified steel slag A. The composite salt solution is a mixed aqueous solution of magnesium nitrate, aluminum nitrate, and calcium nitrate. The mass ratio of magnesium nitrate, aluminum nitrate, calcium nitrate, and doped steel slag is 3.5:8:1.5:200. The concentration of magnesium nitrate in the composite salt solution is 60 g / L.

[0031] The modified steel slag B is prepared as follows: Silane coupling agent KH-550, polyvinyl alcohol, and silicon dioxide are added to the doped steel slag obtained in step S2, and ball-milled for 10 minutes at a speed of 300 rpm with a ball-to-material ratio of 5:1. Zirconia balls are selected, with large, medium, and small ball diameters of 20 mm, 15 mm, and 10 mm, respectively, and a mass ratio of large, medium, and small balls of 2:3:5. Then, the modified steel slag B is obtained by passing it through a 100-mesh sieve, wherein the mass ratio of silane coupling agent KH-550, polyvinyl alcohol, silicon dioxide, and the doped steel slag obtained in step S2 is 1:1:5:100.

[0032] In the above-mentioned preparation method of low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste, the preheating, decomposition and firing temperatures are 700℃, 900℃ and 1000℃ respectively, the mass ratio of dihydrate gypsum to clinker is 0.01:1, and the rest is the same as in Example 1.

[0033] Comparative Example 2 A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste, wherein modified steel slag A is replaced with commercially available steel slag, and the rest is the same as in Example 1.

[0034] Comparative Example 3 A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste, wherein modified steel slag B is replaced with commercially available steel slag, and the rest is the same as in Example 1.

[0035] Comparative Example 4 A low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste, wherein modified steel slag A and modified steel slag B are both replaced with commercially available steel slag, and the rest is the same as in Example 1.

[0036] Table 1. Main chemical components of clinker (%) Table 1 shows the main chemical components of the clinker of this invention.

[0037] Performance testing: The standard consistency water requirement, setting time and soundness of each sample were tested according to GB / T 1346-2024 "Test Method for Standard Consistency Water Requirement, Setting Time and Soundness of Cement"; Samples were prepared and cured according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" and the flexural strength and compressive strength of each sample at (3d, 7d and 28d) were tested.

[0038] Table 2. Water requirements, setting time, and soundness for cement standard consistency Table 3 Strength From Tables 2-3, Figures 1-2 It can be seen that the performance of Comparative Example 1 is worse than that of the Example. The core reason is that its process parameters and raw material ratios deviate from the scope of protection of this invention, which leads to the failure of the modification effect of modified steel slag A and B and the destruction of the synergistic effect of the system. Ultimately, this results in a significant increase in the cement standard consistency water requirement of the cementitious material, abnormal setting time, unqualified stability, and a significant reduction in flexural strength and compressive strength at all ages.

[0039] From Tables 2-3, Figures 1-2 It can be seen that the performance of Comparative Example 2 is reduced. Comparative Example 2 replaced modified steel slag A with commercially available steel slag. However, commercially available steel slag has high content of free calcium oxide and free magnesium oxide, high content of metallic iron, no active silica-alumina layer on the surface, and does not contain calcium fluoride, calcium titanate microcrystals, or magnesium aluminum spinel nanocrystals. When commercially available steel slag is used directly as raw material in the kiln, it cannot effectively reduce the liquid phase viscosity and promote the low-temperature formation of sulfoaluminate minerals at a firing temperature of 1240-1260℃, resulting in insufficient formation of anhydrous calcium sulfoaluminate and tetracalcium aluminoferrite in the clinker, coarse grains, and uneven crystal distribution. In addition, the free oxides in commercially available steel slag remain in the clinker. Although they can be partially eliminated by high-temperature calcination, a small amount of residue still remains, leading to poor stability. Therefore, compared with the example, although the stability of this cementitious material is qualified, the strength at 3d, 7d, and 28d is significantly reduced, the standard consistency water requirement is slightly increased, and the setting time is slightly prolonged.

[0040] From Tables 2-3, Figures 1-2It can be seen that the performance of Comparative Example 3 has decreased. Comparative Example 3 replaced modified steel slag B with commercially available steel slag. Commercially available steel slag has not undergone acid / alkali activation, and its free oxides have not been eliminated, increasing the system's water consumption and affecting stability. It has not undergone ion doping and low-temperature heat treatment, resulting in low self-cementing activity, poor bonding with the cementitious system, and numerous interface defects. Furthermore, the surface of commercially available steel slag lacks an organic-inorganic composite coating layer of silane coupling agent and polyvinyl alcohol, leading to poor interfacial compatibility between particles and the cement matrix. The standard consistency water consumption increases due to the high water absorption and poor dispersibility of the steel slag. Without the filling effect of nano-silica and the early hydration nucleation promoting effect, the cement stone porosity is high, the interfacial transition zone is loose, and although the setting time is extended, the later strength growth is weak. Simultaneously, the residual metallic iron and unstabilized minerals in the commercially available steel slag react slowly in an alkaline environment, potentially causing later volume changes. While the stability is acceptable due to the presence of modified steel slag A, long-term durability is questionable, with a significant decrease in 7-day and 28-day compressive and flexural strength compared to the example.

[0041] From Tables 2-3, Figures 1-2 As can be seen, the performance of Comparative Example 4 decreased significantly. Comparative Example 4 replaced both modified steel slag A and modified steel slag B with commercially available steel slag, effectively losing the core functions of both types of modified steel slag simultaneously. The cumulative effect of these defects led to a significant decline in various performance characteristics. Commercially available steel slag cannot dissolve free oxides, provide nucleation induction, or provide high-temperature resistant seed crystals like modified steel slag A, nor can it improve dispersibility and interfacial bonding performance through interfacial coating like modified steel slag B. This results in the complete loss of the core advantages of the cementitious system. On the one hand, the unmodified commercially available steel slag has poor compatibility and low activity, significantly increasing the water required for cement standard consistency, leading to uneven hydration reactions, abnormal setting time, and potential stability issues. On the other hand, the lack of nucleation induction and interfacial optimization results in incomplete clinker mineral formation, coarse grains, insufficient development of hydration products, and extremely poor system density and interfacial bonding. Ultimately, this leads to a significant decrease in flexural and compressive strength at all ages, with all performance characteristics far below those of the examples, failing to meet the requirements for the use of low-carbon, high-iron sulfoaluminate cementitious materials.

[0042] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-carbon, high-ferric sulfoaluminate cementitious material based on steel slag solid waste, characterized in that, The raw materials include the following parts by weight: limestone 35-55 parts, anhydrite 10-20 parts, bauxite 20-45 parts, modified steel slag A 8-15 parts, and modified steel slag B 5-10 parts. The modified steel slag A is prepared as follows: Step S1: Crush the steel slag, remove iron, then add phosphoric acid solution, react at 50-60℃ for 50-70 minutes, filter after the reaction, add sodium hydroxide solution to the filter cake, react at 70-80℃ for 30-50 minutes, and obtain activated steel slag after post-treatment after the reaction. Step S2: Add calcium fluoride, sodium sulfate and titanium dioxide to activated steel slag and mix for 30-40 min. Then, under inert gas protection, heat to 690-710℃ and hold for 110-130 min. Then cool to room temperature to obtain doped steel slag. Step S3: Add the composite salt solution to the doped steel slag and start stirring. Heat to 75-85℃, adjust the pH to 9.5-10.5, and then continue stirring for 1-2 hours. After the reaction is completed, post-treatment is performed to obtain modified steel slag A.

2. The low-carbon, high-iron sulfoaluminate cementitious material based on steel slag solid waste according to claim 1, characterized in that, In step S1, the mass ratio of phosphoric acid solution to steel slag is 2.5-3.5:1, the concentration of phosphoric acid solution is 9.5-10.5 wt%, the mass ratio of sodium hydroxide solution to filter cake is 2-3:1, and the concentration of sodium hydroxide solution is 7.5-8.5 wt%.

3. The low-carbon high-ferrous sulfoaluminate cementitious material based on steel slag solid waste according to claim 1, characterized in that, The mass ratio of calcium fluoride, sodium sulfate, titanium dioxide, and activated steel slag in step S2 is 0.015-0.025:0.005-0.015:0.003-0.007:

1.

4. The low-carbon high-ferrous sulfoaluminate cementitious material based on steel slag solid waste according to claim 1, characterized in that, The composite salt solution mentioned in step S3 is a mixed aqueous solution of magnesium nitrate, aluminum nitrate, and calcium nitrate. The mass ratio of magnesium nitrate, aluminum nitrate, calcium nitrate, and doped steel slag is 2.5-3.5:7-8:0.5-1.5:100, and the concentration of magnesium nitrate in the composite salt solution is 40-60 g / L.

5. The low-carbon high-ferrous sulfoaluminate cementitious material based on steel slag solid waste according to claim 1, characterized in that, The modified steel slag B is prepared as follows: silane coupling agent KH-550, polyvinyl alcohol, and silicon dioxide are added to the doped steel slag obtained in step S2, ball-milled for 30-60 minutes, and then sieved to obtain modified steel slag B.

6. The low-carbon high-iron sulfoaluminate cementitious material based on steel slag solid waste according to claim 5, characterized in that, The mass ratio of the silane coupling agent KH-550, polyvinyl alcohol, silicon dioxide, and the doped steel slag obtained in step S2 is 1.5-3:0.5-1:2-5:

100.

7. The low-carbon high-ferrous sulfoaluminate cementitious material based on steel slag solid waste according to claim 1, characterized in that, Prepared by the following method: Step (1) grind limestone, bauxite and anhydrite separately until the residue on an 80μm square hole sieve is ≤10%, and then mix them with modified steel slag A to obtain raw material; Step (2) involves preheating, decomposing, and calcining the raw materials in sequence, followed by cooling, and then discharging the cooked materials to obtain the clinker. Step (3) Grind the clinker to a specific surface area of ​​330-360 m². 2 / kg, add modified steel slag B and dihydrate gypsum, and grind together to a specific surface area of ​​420-460m². 2 / kg, that is, the result.

8. The low-carbon high-ferrous sulfoaluminate cementitious material based on steel slag solid waste according to claim 7, characterized in that, The temperatures for preheating, decomposition, and firing in step (2) are 790-810℃, 1090-1110℃, and 1240-1260℃, respectively.

9. The low-carbon high-ferrous sulfoaluminate cementitious material based on steel slag solid waste according to claim 7, characterized in that, The mass ratio of dihydrate gypsum and clinker in step (3) is 0.03-0.08:1.

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