A steel slag modified cementitious material, preparation method and application

Abstract

The present invention belongs to the technical field of solid waste resource utilization, and discloses a steel slag modified cementitious material, a preparation method and an application thereof. The preparation method comprises the following steps: S1, collecting high-temperature steel slag; S2, regulating the components of molten steel slag under heat preservation; S3, modifying and reconstructing the phase of the material in the heat preservation stage; S4, reconstructing the phase of the modified steel slag in the first-stage cooling; S5, reconstructing the phase of the modified steel slag in the second-stage cooling; S6, post-treatment after cooling. By synchronously improving the formula and the preparation process, directly treating the molten steel slag, and combining the heat preservation and the phase reconstruction of two-stage cooling with modification, the present invention controls the content of each component and the phase such as crystal grains in the steel slag, so that it meets the requirements of the new national standard at the same time, and enables the treated modified material to be used as clinker, applied to the manufacture of ordinary portland cement, and increase the consumption amount. The present invention simultaneously utilizes energy and resources, improves the resource utilization value and the total consumption amount of steel slag, and has high application value in industry.

Description

Technical Field

[0001] The present invention relates to the technical fields of solid waste resource utilization and metallurgy, and specifically relates to a steel slag modified cementitious material, a preparation method and an application thereof. Background Art

[0002] Steel slag is an industrial waste and one of the large amounts of solid wastes that are difficult to treat and utilize in the metallurgical industry. In recent years, with the continuous increase in steel production, as a by-product in the steelmaking process, the output of steel slag has also increased sharply. At present, most steel enterprises only stay at the stage of preliminary crushing and magnetic separation to recover iron from steel slag, while most of the steel slag tailings are directly stacked, which not only pollutes the environment, but also occupies a large amount of land resources, and at the same time is a waste of resources for steel slag.

[0003] Steel slag contains cementitious minerals tricalcium silicate (3CaO·SiO2) and dicalcium silicate (2CaO·SiO2), so steel slag is also commonly used in cement, concrete and other aspects. However, due to the small amount of silicate minerals and large crystal grains in steel slag, its cementitious activity is poor, so the activity of steel slag is far lower than that of cement clinker. But with the promulgation and implementation of the new national standard GB 175-2023, steel slag can no longer be directly used as a cement admixture, reducing the utilization ways of steel slag. In addition, the current application ways of steel slag are to use it after natural cooling to room temperature, while the discharge temperature of steel slag is as high as 1600°C, and a large amount of heat energy is not effectively utilized.

[0004] In the existing patent technology, a method for reducing and recovering iron from steel slag and preparing an auxiliary cementitious material from secondary slag disclosed in Chinese invention document CN108658483A is to mix converter steel slag (cooled to room temperature), a reducing agent and a component adjusting material evenly, then heat and calcine separately, melt back under a high-temperature reducing atmosphere, and then water-quench and cool. After separating metallic iron, the secondary slag is dried and ground to obtain an auxiliary cementitious material. This technical solution requires additional energy for melting back (the melting-back calcination temperature is 1455-1495°C), and cannot utilize the waste heat of molten steel slag itself, with high energy consumption; the crystal development particle size of the composition in the steel slag cannot be controlled during direct water-quenching and cooling, so only an auxiliary cementitious material can be obtained, and it cannot directly replace cement clinker.

[0005] A method for preparing fine powder by smelting and tempering steel slag disclosed in Chinese invention patent document CN115745449A. After thoroughly stirring and mixing the steel slag with acidic oxides, a reducing agent is added and then stirred and mixed to obtain a steel slag mixture. Then, the steel slag mixture is added to a smelting furnace and smelted until the steel slag mixture becomes liquid. Then, the tempering slag solution at 1500 °C is rapidly frozen and cooled to below 50 °C within 10 - 15 s, and the cooling rate is 96 - 145 °C / s. The purpose of cooling is to shorten the waiting time for the natural cooling of the tempering slag and quickly obtain low-temperature tempering slag for further processing into fine powder and emptying the container for the next batch of steel slag processing, rather than to adjust the grain size of the internal components of the tempering slag.

[0006] In other documents, the existing patent technology CN104016600A discloses a method of using silicon-rich materials to reconstruct and modify steel slag at high temperature and then separating iron by magnetic separation. By adding silicon-rich materials for high-temperature reconstruction and modification, the volume stability and cementitious activity of the steel slag are improved. Then, iron minerals are separated by magnetic separation, and those with high iron content can be used as raw materials for iron smelting. However, this method fails to fully utilize the heat of the steel slag and still achieves the purpose of steel slag modification through secondary heating and calcination, and the properties of its products cannot directly replace cement clinker. Another invention patent CN111996314A discloses a method for extracting iron from carbon thermal reduction of hot converter slag, ensuring that the tapping temperature of the converter is above 1600 °C. After tapping, coke powder and hot converter slag are mixed in batches in a slag ladle, and then nitrogen is blown for stirring. At the same time, river sand is added in batches to modify the converter slag, and more than 80% of the iron oxides in the converter slag can be reduced to metallic iron. Although this method utilizes the heat of the converter slag, the reduction degree of iron is not complete enough and the recovery rate is low. Moreover, it is proposed that the modified converter slag can be used in slag cement (not ordinary Portland cement) to replace part of the cement clinker, and the application field is relatively limited. The third invention patent CN106348626A discloses a method for recovering molten converter steel slag to produce concrete admixtures, which aims to improve the cementitious activity of the steel slag and recycle the steel slag by adding ferrosilicon as a reducing agent. The cost of the reducing agent ferrosilicon used in this method is relatively high, and it can only be used as a concrete admixture in application, with low value. The fourth invention patent CN102796833A discloses a modification process for melting steel slag iron reduction and its component reconstruction, which modifies the steel slag by adding coke and silica in the molten steel slag. However, this method still needs to reheat the mixed steel slag, and the prepared glass-ceramic pellets are not proposed. Although the application range is large, the actual total consumption is far less than that of cement, which limits the industrial consumption capacity of a large amount of steel slag.

[0007] In summary, with the promulgation and implementation of the new national standard GB 175-2023, existing technologies can no longer consume and resourcefully utilize a large amount of solid waste steel slag; moreover, existing technologies cannot maximize the comprehensive utilization of the "heat" of newly molten steel slag, the "iron" in the steel slag, and the "slag" resource after iron removal simultaneously, while meeting the industrial requirements for low-cost, high-value resource utilization of steel slag and expanding the total consumption volume. Summary of the Invention

[0008] The object of the present invention is to overcome the above technical deficiencies and provide a preparation method and application of a steel slag modified cementitious material. By synchronously improving the formula and preparation process, directly transporting and treating the molten steel slag using an intermediate slag pot, and adopting a method of heat preservation combined with two-stage cooling for phase reconstruction modification to control the growth of the steel slag phase grains in the modified cementitious material, making the composition and particle size of each component approximately similar to those of cement clinker. At the same time, controlling the content of each component within the range required by the new national standard GB / T 21372-2024 for Portland cement clinker (including the content of free calcium oxide, etc.), enabling the modified material to be supplied to cement plants as cement clinker and increasing the consumption volume; reducing more than 97wt% of the iron-containing oxides in the molten steel slag to metallic iron and modifying other components into cementitious materials, thereby realizing the synchronous comprehensive utilization of high value, resource utilization, and large consumption volume of the "heat", "iron", and "slag" resources in the molten steel slag, so as to solve problems such as energy waste, low utilization rate of solid waste steel slag, land occupation by stacking, and environmental pollution in the metallurgical industry.

[0009] To achieve the above technical objectives, the technical solution provided by the present invention is as follows:

[0010] A preparation method of a steel slag modified cementitious material, characterized in that it includes the following steps:

[0011] S1. Collect high-temperature steel slag

[0012] Use a heat-insulated intermediate slag pot to collect the high-temperature molten steel slag (about 1700°C) discharged from the steelmaking converter and transport it to the modification treatment workshop;

[0013] S2. Regulation of molten steel slag components under heat preservation

[0014] Keep the temperature of the steel slag in the slag pot in a molten state at 1500~1600°C. After adding the pre-prepared modified powder to the molten steel slag and mixing and stirring, during the stirring process, Ca 2+ ions diffuse and react with silicate ions and 2CaO·SiO2 to carry out phase reconstruction, forming the main phase 3CaO·SiO2 of Portland cement. At the same time, the iron-containing phase in the molten steel slag reacts with the reducing agent in the modified powder to generate elemental iron;

[0015] The modified powder material is a mixed powder composed of a reducing agent, a calcareous material, and a siliceous material with a set ratio and a particle diameter of 5 - 50 mm. The mass ratio of each component is reducing agent: calcareous material: siliceous material: molten steel slag = (0.08 - 0.18):(0.12 - 0.23):(0.018 - 0.055):1;

[0016] S3. Phase modification and reconstruction during the heat preservation stage

[0017] Stop stirring and continue to maintain the temperature of the molten steel slag in the slag pot at 1500 - 1600 °C in a molten state for 30 - 60 minutes to homogenize the composition of the molten steel slag. During this process, the molten iron reduced naturally settles to the bottom of the slag pot, and the molten modified steel slag after fractional regulation naturally floats on the upper part of the slag pot; transfer the molten modified steel slag that naturally floats on the upper part of the slag pot to another heat-preserved slag pot for modification to separate the slag and iron;

[0018] S4. Phase reconstruction during the first-stage cooling of the modified steel slag

[0019] For the molten modified steel slag with a temperature of 1500 - 1600 °C after transfer, control the slow cooling of the modified steel slag to 1250 - 1300 °C at a rate of 10 - 30 °C / min for the first-stage cooling phase reconstruction. During this process, the main phases of cement clinker, 3CaO·SiO2 and 2CaO·SiO2, precipitate from the molten modified steel slag, and small crystals gradually grow and develop;

[0020] S5. Phase reconstruction during the second-stage cooling of the modified steel slag

[0021] Control the rapid cooling of the modified steel slag from 1250 - 1300 °C to room temperature at a cooling rate of 40 - 70 °C / s. During this process, the growth of the formed 3CaO·SiO2 crystals stops, the 3CaO·SiO2 crystals are of moderate size, the decomposition of the 3CaO·SiO2 phase is inhibited, and the polymorphic transformation of 2CaO·SiO2 into the γ form is prevented, enabling the components of the molten modified steel slag to interact with each other and gradually form the main phases contained in cement clinker, 3CaO·SiO2 and 2CaO·SiO2;

[0022] S6. Post-treatment after cooling

[0023] Cool the product of step S5 to room temperature to obtain a block-shaped steel slag modified cementitious material that has undergone heat preservation and two-stage cooling phase reconstruction. First, crush it and then grind it until the specific surface area SSA reaches 300 m² / kg ≤ SSA ≤ 400 m² / kg to prepare a Portland cement clinker mainly composed of phases such as 3CaO·SiO2 and 2CaO·SiO2.

[0024] A steel slag modified cementitious material is prepared by the said method. The contents of various components and the physical phases such as crystal grain size in this steel slag modified cementitious material are all controlled within the range required by the new national standard GB / T 21372-2024 for Portland cement clinker (including the content of free calcium oxide, etc.).

[0025] The application of the said steel slag modified cementitious material as clinker in the preparation of ordinary Portland cement can directly replace the ordinary Portland cement clinker under the specification of GB / T 21372-2024. After grinding with auxiliary materials such as gypsum, it can be directly used as cement.

[0026] Compared with the prior art, the beneficial effects of the present invention include:

[0027] 1. The steel slag modified cementitious material, preparation method and application provided by the present invention, through the synchronous improvement of the formula and preparation process, adopt the direct treatment of molten steel slag, and through the method of phase reconstruction and modification by heat preservation and two-stage cooling, control the contents of various components and the physical phases such as crystal grains in the steel slag, so that the various components of the molten steel slag and the modified powder interact with each other and gradually form the main physical phases 3CaO·SiO2 and 2CaO·SiO2 contained in cement clinker, making the physical phase composition of the steel slag component and crystal grain size, etc. in the modified cementitious material approximate to the physical phase of cement clinker, and can control the contents of various components in the powder steel slag modified cementitious material to meet the requirements for the fineness of Portland cement in GB 175-2023 General Portland Cement, enabling the treated modified material to be used as clinker, applied in the manufacture of ordinary Portland cement, and improving the consumption volume.

[0028] 2. The steel slag modified cementitious material, preparation method and application provided by the present invention use two slag pots to transfer and modify the molten steel slag respectively, without the need for secondary heating and calcination. Using the waste heat of the steel slag, more than 97wt% of the iron oxides in the molten steel slag can be reduced to metallic iron, and the other part is prepared into a modified cementitious material, so as to realize the synchronous comprehensive utilization of "heat", "iron" and "slag" with high value, resource utilization and large consumption volume, and can simultaneously solve problems such as energy waste, low utilization rate of solid waste steel slag, occupation of land by stacking and environmental pollution in the metallurgical industry.

[0029] 3. Through the coordinated cooperation of components, formulation, and process, the present invention can efficiently utilize the waste heat and various minerals of molten steel slag simultaneously. During the high-temperature modification stage, modified powder materials are added to regulate the phase of the steel slag, and then three-stage phase modification of heat preservation, slow cooling, and rapid cooling is carried out. The cementitious materials in the upper part of the slag pot after separation can be applied to the cement field, and the iron resources recovered from the lower part of the slag pot can be re-input into the production of the steel plant. Therefore, it can effectively reduce energy waste, and at the same time, it also reduces the waste of land resources and environmental pollution problems caused by the stacking of steel slag. On the one hand, it comprehensively utilizes energy and resources, which is beneficial to the industrialized and large-scale treatment of steel slag solid waste, and can also achieve carbon emission reduction in the high-energy-consuming iron and steel metallurgy industry.

[0030] 4. The modification treatment method of the molten steel slag of the present invention is simple and the process is scientific. The used slag pot is an existing device. By mixing and stirring the reducing agent, calcareous material, and siliceous material with the molten steel slag to make the components uniform, and then using the waste heat of the molten steel slag to carry out a carbothermal reduction reaction, the modified molten steel slag in the upper part is obtained in the slag pot, and the reduced molten iron completely settles to the bottom of the slag pot due to its large density, and the automatic separation of slag and iron can be achieved during the heat preservation stage; in the present invention, the calcareous material, siliceous material, and steel slag are mixed and stirred in the slag pot to fully react with components such as silicon dioxide in the steel slag, so as to increase the content of cementitious minerals in the steel slag and form phase-modified steel slag. And by controlling the reduction rate, mainly 3CaO·SiO2 and 2CaO·SiO2 are generated, and the content of each component can be controlled within the range required by the new national standard GB / T 21372-2024 for Portland cement clinker (including the content of free calcium oxide, etc.), so that it can be supplied to the cement plant as Portland cement clinker and can replace Portland cement clinker, greatly improving the total consumption and application value of steel slag.

[0031] 5. The present invention reduces the iron phase in the steel slag by adding reducing agent coke particles, activated carbon, carbon pitch, and graphite product recycling materials to the molten steel slag; adding calcareous material calcium oxide to reduce the viscosity, and the increase in liquid phase amount can promote the formation of 3CaO·SiO2. At the same time, the calcareous material will consume silicon dioxide in the steel slag to generate 3CaO·SiO2, thereby increasing the cementitiousness of the modified steel slag; adding a small amount of siliceous materials such as quartz sand, silica fume, and quartz waste to adjust the mineral composition, which can react with the excess calcareous material that has not reacted with the steel slag to generate 3CaO·SiO2. During the cooling process of the upper modified steel slag, part of 3CaO·SiO2 will decompose to generate 2CaO·SiO2 and free calcium oxide. Therefore, by controlling the cooling rate, its decomposition degree is controlled, and the cementitious material is directly obtained after cooling, while the reduced molten iron settles to the bottom of the slag pot due to its large density and can be efficiently recycled.

[0032] 6. The present invention combines the resource utilization of solid waste with metallurgical technology, providing a method for high-temperature phase reconstruction and modification of molten steel slag with low cost, high value, and large consumption capacity, as well as high-value materials. By pouring molten steel slag into a slag ladle, adding modified powder materials into the slag ladle, mixing and stirring, then insulating and performing high-temperature melting modification, after the reduced iron completely settles to the bottom of the slag ladle, the modified molten steel slag in the upper part is obtained. Pour the modified molten steel slag into a slag ladle (or other heat-insulating containers), control its heat preservation time and cooling rate to carry out three-stage continuous phase modification. After cooling to room temperature, a block-shaped cementitious material with component content and grain size both meeting the requirements can be directly obtained. During this process, the iron settled at the bottom of the slag ladle can be recycled first and used in steel production. The present invention recovers almost all iron elements in the steel slag, reduces more than 97wt% of the iron-containing oxides in the steel slag into metallic iron, synchronously adjusts the phase composition and grain size of the steel slag, makes the phase composition of the modified steel slag close to that of cement clinker, and obtains a low-cost and high-performance cementitious material that can replace the Portland cement clinker in GB / T 21372-2024, having high utilization value in industry.

[0033] 7. The preparation method provided by the present invention can realize three-stage phase reconstruction of molten steel slag, make the phase composition of the modified steel slag gel material close to that of cement clinker, and the prepared cement product meets the requirements for general Portland cement in GB 175-2023 standard. At the same time, it can reduce more than 97wt% of the iron-containing oxides in the molten steel slag into metallic iron. It uses fewer equipment, has simple process steps, is easy to control, has stable quality, is easy to industrialize, has a large consumption capacity, and can efficiently utilize energy and resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of XRD test of the steel slag raw material in the embodiment of the present invention and the original steel slag and the prepared steel slag modified cementitious material used in Examples 1-5;

[0035] Figure 2 It is a schematic diagram of BSE test of the steel slag modified cementitious material prepared in Example 3 of the present invention;

[0036] Figure 3 It is a schematic diagram of XRD test of the steel slag modified cementitious material prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following further elaborates the present invention in detail with reference to the drawings and multiple specific embodiments, so that those skilled in the art can implement it according to the description in the specification.

[0038] It should be understood that the terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0039] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or prepared by existing methods.

[0040] Basic Example

[0041] The preparation method of the steel slag modified cementitious material provided in this example includes the following steps:

[0042] S1. Collect high-temperature steel slag

[0043] Use a heat-insulated intermediate slag ladle to collect the high-temperature molten steel slag (about 1700 °C) discharged from the steelmaking converter and transport it to the modification treatment workshop;

[0044] The steel slag is ordinary converter molten steel slag, and its total iron content is 20 - 40 wt%.

[0045] S2. Regulation of molten steel slag components under heat preservation

[0046] Keep the temperature of the steel slag in the slag ladle in a molten state at 1500 - 1600 °C. After adding the pre-prepared modification powder to the molten steel slag, mix and stir. The stirring speed is 10 - 50 r / min, and the stirring time is 10 - 60 min; during the stirring process, Ca 2+ ions diffuse and react with silicate ions and 2CaO·SiO2 to carry out phase reconstruction to form the main phase 3CaO·SiO2 of portland cement. At the same time, the iron-containing phase in the molten steel slag reacts with the reducing agent in the modification powder to generate elemental iron;

[0047] The modification powder is a mixed powder composed of a reducing agent, a calcareous material, and a siliceous material with a set ratio and a particle diameter of 5 - 50 mm. The mass ratio of each component is reducing agent: calcareous material: siliceous material: molten steel slag = (0.08 - 0.18): (0.12 - 0.23): (0.018 - 0.055): 1;

[0048] The reducing agent is one or more of coke particles, activated carbon, carbon pitch, and graphite product recycling materials, and the carbon content is ≥ 85 wt%.

[0049] The calcareous material component in the modification powder contains calcium oxide, and the content of calcium oxide is 90 - 100 wt%.

[0050] The siliceous material in the modification powder is one or more of quartz sand, silica fume, and quartz waste, and the content of silicon dioxide is 90 - 100 wt%.

[0051] S3. Phase modification and reconstruction during the heat preservation stage

[0052] Stop stirring and continue to keep the molten state of the steel slag in the slag pot at 1500 - 1600 °C for 30 - 60 minutes of heat preservation time to homogenize the composition of the molten steel slag. During this process, the molten iron reduced naturally settles to the bottom of the slag pot, and the molten modified steel slag after adjustment naturally floats on the upper part of the slag pot; transfer the molten modified steel slag that naturally floats on the upper part of the slag pot to another heat-preserved slag pot for modification to separate the slag and iron; after the heat preservation ends and the slag and iron are separated, recover the molten iron that naturally settles at the bottom of the slag pot and reuse it for steel production;

[0053] In the process of high-temperature molten phase modification and reconstruction in this step, the calcareous material and siliceous material in the modified powder are continuously dissolved and diffused by heat. Mixing and stirring make the mixing of the modified powder and steel slag more uniform. In the molten state, Ca 2+ ions diffuse and react with silicate ions and 2CaO·SiO2 to form the main phase 3CaO·SiO2 of portland cement; at the same time, due to the addition of the calcareous material, the viscosity of the system decreases, and the diffusion rate of the particles in the liquid phase increases, which is beneficial to the formation of 3CaO·SiO2 and also beneficial to the reaction between the iron-containing phase in the molten steel slag and the reducing agent in the modified material to generate elemental iron; in this process, the chemical composition of the molten steel slag is regulated by the modified powder, so that the iron element sinks to the bottom of the slag pot in the form of elemental iron, and the remaining chemical composition is close to the chemical composition of cement clinker;

[0054] S4. Phase reconstruction of the first-stage cooling of the modified steel slag

[0055] For the molten modified steel slag with a temperature of 1500 - 1600 °C after transfer, use the air-cooling method (natural cooling) to control the slow cooling of the modified steel slag to 1250 - 1300 °C at a rate of 10 - 30 °C / min for the first-stage cooling phase reconstruction. During this process, the main phases 3CaO·SiO2 and 2CaO·SiO2 of the cement clinker precipitate from the molten modified steel slag, and the small crystals gradually grow and develop;

[0056] S5. Phase reconstruction of the second-stage cooling of the modified steel slag

[0057] Adopt the air-cooling method (blowing cold air into the slag pot) to control the rapid cooling of the modified steel slag from 1250 - 1300 °C to room temperature at a cooling rate of 40 - 70 °C / s. In this process, the growth of the generated 3CaO·SiO2 crystals stops, the grains of 3CaO·SiO2 are moderate, the decomposition of the 3CaO·SiO2 phase is inhibited, and the polymorphic transformation of 2CaO·SiO2 into the γ-type is prevented. The various components of the molten modified steel slag interact with each other and gradually form the main phases 3CaO·SiO2 and 2CaO·SiO2 contained in the cement clinker;

[0058] S6. Post-treatment after cooling

[0059] Cool the product of step S5 to room temperature to obtain the bulk steel slag modified cementitious material with heat preservation and two-stage cooling for phase reconstruction. First, crush it and then grind it until the specific surface area SSA reaches 300 m² / kg ≤ SSA ≤ 400 m² / kg, thus preparing the Portland cement clinker mainly composed of phases such as 3CaO·SiO2 and 2CaO·SiO2.

[0060] During the process of phase modification and reconstruction during the cooling process in steps S4 - S5, during the controlled cooling process, the main phases of the cement clinker, such as 3CaO·SiO2 and 2CaO·SiO2, are precipitated from the molten steel slag. By controlling the cooling rate, the grains of 3CaO·SiO2 are made moderate, the decomposition of the 3CaO·SiO2 phase is inhibited, and the crystal form transformation of 2CaO·SiO2 into the γ-type is prevented. This process gradually forms the main phases such as 3CaO·SiO2 and 2CaO·SiO2, their component contents, and grain sizes that meet the requirements of the cement clinker in the molten modified steel slag, so as to improve the strength of the cement.

[0061] A steel slag modified cementitious material is prepared by the aforementioned method. The content of each component and the grain size and other phases in the steel slag modified cementitious material are all controlled within the range required by the new national standard GB / T 21372 - 2024 for Portland cement clinker (including the content of free calcium oxide, etc.).

[0062] The application of the described steel slag modified cementitious material as a clinker in the preparation of ordinary Portland cement can directly replace the ordinary Portland cement clinker under the specification of GB / T 21372 - 2024. After grinding with auxiliary materials such as gypsum, it is prepared into ordinary Portland cement and directly used as cement. Specifically, in the bulk steel slag modified cementitious material obtained after cooling in step S6, add auxiliary materials such as gypsum and grind them together until it meets the fineness requirements for Portland cement in GB 175 - 2023 General Portland Cement, then the finished product of ordinary Portland cement can be directly obtained.

[0063] To more clearly understand the purpose, technical solution, and advantages of the present invention, the following further details the present invention in combination with multiple specific examples based on the above basic examples. The specific data involved in the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0064] The converter steel slag used in the following examples is taken from steel enterprises (such as Baosteel and Magang). According to the standard of YB / T 148 - 2015 "Determination Method for Total Iron Content in Steel Slag", its total iron content is 20 - 40 wt%; each component in the modified powder is a commercially available product; the slag pot adopts the existing conventional slag pot.

[0065] Example 1

[0066] The steel slag modified cementitious material, preparation method and application provided in this embodiment are specific applications based on the foregoing basic embodiment; the converter steel slag used in this embodiment is taken from Baosteel Group, and its total iron content is about 25wt% on average.

[0067] The preparation method of the steel slag modified cementitious material provided in this embodiment is basically the same as that of the basic embodiment, and specifically further includes the following steps:

[0068] Pre-prepare modified powder materials, and the components and mass ratios in the modified powder materials are reducing agent: calcareous material: siliceous material: molten steel slag = 0.10: 0.12: 0.018: 1, where the particle diameters of each component are all greater than 5mm and not greater than 50mm (D 50 = 45mm);

[0069] The reducing agent therein is a mixture of coke particles with a carbon content ≥ 85wt% and recycled graphite product materials, configured according to a mass ratio of 1:1; the coke particles are produced by Gongyi Xinjiayuan Water Purification Materials Co., Ltd., and the recycled graphite product materials are recycled graphite crucible materials from Baofeng Graphite Products Factory;

[0070] The calcareous material is calcium oxide produced by Fuchen Tianjin Chemical Reagent Co., Ltd. with a calcium oxide content of 90wt%. In other embodiments, other compounds or mixtures containing 90wt% calcium oxide as the main component can also be used.

[0071] The siliceous material is quartz sand produced by Tianjin Zhonglian Chemical Reagent Co., Ltd., in which the silicon dioxide content is 90wt%.

[0072] S1. Collect high-temperature steel slag

[0073] Use a conventional heat-insulated intermediate slag pot (with a volume of 16 cubic meters) to collect the high-temperature molten steel slag discharged from the steelmaking converter at about 1700°C. Pour the molten steel slag from the converter into the slag pot, and then transport it to the modification treatment workshop;

[0074] S2. Regulation of molten steel slag components under heat preservation

[0075] Keep the temperature of the steel slag in the slag pot in a molten state at 1500~1600°C. After adding the pre-prepared modified powder materials to the molten steel slag, mix and stir. The stirring speed is 30 r / min, and the stirring time is 40 min;

[0076] S3. Phase modification and reconstruction during the heat preservation stage

[0077] After reaching the set stirring time, stop stirring and continue to keep the molten state of the steel slag in the slag pot at 1500-1600 °C for 60 minutes of heat preservation to homogenize the composition of the molten steel slag; after the heat preservation ends and the slag and iron are separated, recover the molten iron that naturally settles at the bottom of the slag pot and reuse it for iron and steel production. Transfer the molten modified steel slag that naturally floats on the upper part of the slag pot to another heat-preserved slag pot for modification;

[0078] S4. Reconstruction of the first-stage cooling phase of the modified steel slag

[0079] For the molten modified steel slag with a temperature of 1500-1600 °C after transfer, adopt the air-cooling method (natural cooling) and control the slow cooling of the modified steel slag to 1250-1300 °C at a rate of 10-30 °C / min for the first-stage cooling phase reconstruction. During this process, the main phases of the cement clinker, 3CaO·SiO2 and 2CaO·SiO2, precipitate from the molten modified steel slag, and small crystals gradually grow and develop;

[0080] S5. Reconstruction of the second-stage cooling phase of the modified steel slag

[0081] After the modified steel slag is slowly cooled to 1250-1300 °C, then adopt the air-cooling method (blowing cold air into the slag pot) and control the rapid cooling of the modified steel slag from 1250-1300 °C to room temperature at a cooling rate of 50 °C / s. This process stops the continuous growth of the generated 3CaO·SiO2 grains, makes the 3CaO·SiO2 grains moderate, inhibits the decomposition of the 3CaO·SiO2 phase and prevents the polymorphic transformation of 2CaO·SiO2 into the γ form, and enables the components of the molten modified steel slag to interact with each other and gradually form the main phases contained in the cement clinker, 3CaO·SiO2 and 2CaO·SiO2;

[0082] S6. Post-treatment after cooling

[0083] Cool the blocky steel slag modified cementitious material obtained in step S5 to room temperature after heat preservation and two-stage cooling phase reconstruction, first crush it and then grind it to a specific surface area of 300 m² / kg ≤ SSA ≤ 400 m² / kg to prepare a Portland cement clinker mainly composed of phases such as 3CaO·SiO2 and 2CaO·SiO2. Gypsum and other auxiliary materials can also be added to the blocky steel slag modified cementitious material and then ground together to meet the fineness requirements of Portland cement in the national standard GB 175-2023 for general Portland cement, that is, to prepare a Portland cement product.

[0084] In the above embodiments of the present invention, the key is to reconstruct and modify the phase of molten steel slag through heat preservation and two-stage cooling, so that the prepared cementitious material can replace the Portland cement clinker in GB / T 21372-2024. When gradually increasing the addition amount of the modified powder, the calcium oxide content in the system rises, the alkalinity increases, the viscosity decreases, the liquid phase amount increases, the molecular mobility is high, and the ion diffusion ability is strong. At the same time, in the preparation process of the present invention, the mixing and stirring steps also make each component more uniform, promoting the reaction of 2CaO·SiO2 in the modified steel slag with calcium oxide to generate 3CaO·SiO2, so that the content of 3CaO·SiO2 gradually increases. And the present invention controls the cooling rate and reduces the decomposition of 3CaO·SiO2 into 2CaO·SiO2, so that the RO phase solid solution in the steel slag is decomposed and reacted, and the decomposed products are MgO and iron oxides (FeOx); FeOx decomposed from the RO phase solid solution and Ca2Fe2O5 in the steel slag are reduced to molten iron by the reducing agent in the modified powder, and naturally settle to the bottom of the slag pot under the action of gravity, separating from the slag, which is convenient for recycling; also, due to the increase in calcium oxide content, a certain amount of 3CaO·Al2O3 is formed by the reaction of a small amount of aluminum-containing components in the steel slag with calcium oxide.

[0085] The properties of the steel slag and the prepared steel slag modified cementitious material used in this example are shown in the appendix Figure 1 The chemical composition of the prepared steel slag modified cementitious material is shown in Table 2, and the results of the iron reduction rate and the free calcium oxide content are shown in Table 1.

[0086] Example 2

[0087] The steel slag modified cementitious material, preparation method and its application provided in this example are also specific applications based on the foregoing basic examples, which are basically the same as those in Example 1. The differences in the preparation steps S1-S6 from those in Example 1 are as follows:

[0088] Prepare the modified powder in advance. The components and mass ratios in the modified powder are reducing agent: calcareous material: siliceous material: molten steel slag = 0.10:0.17:0.037:1, and the particle diameters of each component are not more than 50 mm (D50 = 40 mm);

[0089] The reducing agent is a mixture of commercially available coke particles (Gongyi Xinjiayuan Water Purification Materials Co., Ltd.) with a total carbon content ≥ 87.5 wt% and recycled graphite products (produced by Baofeng Graphite Products) in a mass ratio of 2:1;

[0090] The calcareous material is commercially available calcium oxide with a calcium oxide content of 95 wt%;

[0091] The siliceous material is silica fume with a silica content of 95 wt%, specifically 92 ordinary silica fume produced by Beijing Zhengyuan Yiqing New Materials Technology Co., Ltd.;

[0092] In the preparation method of this embodiment, the differences are as follows:

[0093] S2. Regulation of molten steel slag components under heat preservation

[0094] Keep the temperature of the steel slag in the slag ladle in a molten state at 1500 - 1600 °C. After adding the pre-prepared modified powder to the molten steel slag, mix and stir. The stirring speed is 20 r / min, and the stirring time is 50 min;

[0095] S3. Phase modification and reconstruction during the heat preservation stage

[0096] After reaching the set stirring time, stop stirring and continue to keep the temperature of the steel slag in the slag ladle in a molten state at 1500 - 1600 °C. The heat preservation time is 55 min to make the composition of the molten steel slag uniform; after the heat preservation ends and after the slag and iron are separated, recover the molten iron that naturally settles at the bottom of the slag ladle and reuse it for steel production. Transfer the molten modified steel slag that naturally floats on the upper part of the slag ladle to another heat-preserved slag ladle for modification;

[0097] S4. Phase reconstruction during the first-stage cooling of the modified steel slag

[0098] For the molten modified steel slag with a temperature of 1500 - 1600 °C after transfer, use the air-cooling method (natural cooling) to control the slow cooling of the modified steel slag to 1250 - 1300 °C at a rate of 10 - 30 °C / min for the first-stage cooling phase reconstruction. During this process, the main phases of cement clinker, 3CaO·SiO2 and 2CaO·SiO2, precipitate from the molten modified steel slag, and the small crystals gradually grow and develop;

[0099] S5. Phase reconstruction during the second-stage cooling of the modified steel slag

[0100] After the modified steel slag is slowly cooled to 1250 - 1300 °C, then use the air-cooling method to control the rapid cooling of the modified steel slag from 1250 - 1300 °C to room temperature at a cooling rate of 60 °C / s.

[0101] The other contents of the preparation method, materials and applications of this embodiment are the same as those of Embodiment 1. For the steel slag used and the properties of the prepared steel slag modified cementitious material, see the appendix Figure 1 , the chemical composition of the prepared steel slag modified cementitious material is shown in Table 2, and the results of the iron reduction rate and the free calcium oxide content are shown in Table 1.

[0102] Embodiment 3

[0103] The steel slag modified cementitious material, preparation method and its application provided in this embodiment are also specific applications based on the foregoing basic embodiment, which are basically the same as those in Embodiment 1. The differences in the preparation steps S1 - S6 from those in Embodiment 1 are as follows:

[0104] Pre-prepare modified powder materials. The components and mass ratios in the modified powder materials are as follows: reducing agent: calcareous material: siliceous material: molten steel slag = 0.10:0.23:0.055:1, and the particle diameters of each component are not greater than 45 mm (D 50 = 35 mm);

[0105] The reducing agent is a mixture prepared from activated carbon with a carbon content of ≥89.5 wt% and carbon pitch in a mass ratio of 1:1;

[0106] The calcareous material is calcium oxide produced by Shanghai Huake Experimental Equipment Co., Ltd. with a calcium oxide content of 99.95 wt%;

[0107] The siliceous material is quartz sand produced by Xi'an Yizhichen Biotechnology Co., Ltd., and the content of silicon dioxide in it is 99.7 wt%.

[0108] In the preparation method of this embodiment, the differences are as follows:

[0109] S2. Regulation of molten steel slag components under heat preservation

[0110] Keep the temperature of the steel slag in the slag pot in a molten state at 1500 - 1600 °C. After adding the pre-prepared modified powder materials to the molten steel slag, mix and stir. The stirring speed is 30 r / min, and the stirring time is 45 min;

[0111] S3. Phase modification and reconstruction in the heat preservation stage

[0112] After reaching the set stirring time, stop stirring and continue to keep the temperature of the steel slag in the slag pot in a molten state at 1500 - 1600 °C. The heat preservation time is 60 min to make the components of the molten steel slag uniform; after the heat preservation ends and after the slag and iron are separated, recover the molten iron that naturally settles at the bottom of the slag pot and reuse it for steel production. Transfer the molten modified steel slag that naturally floats on the upper part of the slag pot to another heat-preserved slag pot for modification;

[0113] S4. Phase reconstruction during the first-stage cooling of modified steel slag

[0114] For the molten modified steel slag with a temperature of 1500 - 1600 °C after transfer, use the air-cooling method (natural cooling) to control the slow cooling of the modified steel slag to 1250 - 1300 °C at a speed of 10 - 30 °C / min for the first-stage cooling phase reconstruction. During this process, the main phases of cement clinker, 3CaO·SiO2 and 2CaO·SiO2, precipitate from the molten modified steel slag, and small crystals gradually grow and develop;

[0115] S5. Phase reconstruction during the second-stage cooling of modified steel slag

[0116] After the modified steel slag is slowly cooled to 1250 - 1300 °C, the air cooling method is then adopted, and at a cooling rate of 55 °C / s, the modified steel slag is rapidly cooled from 1250 - 1300 °C to room temperature.

[0117] For other contents of the preparation method, materials and applications in this example, they are the same as those in Example 1. For the steel slag used and the properties of the prepared steel slag modified cementitious material, see the appendix Figure 1 , the chemical composition of the prepared steel slag modified cementitious material is shown in Table 2, and the results of the iron reduction rate and the free calcium oxide content are shown in Table 1.

[0118] Example 4

[0119] The steel slag modified cementitious material, preparation method and its application provided in this example are also specific applications based on the foregoing basic examples. The basic contents of the preparation method, materials and applications in this example are all the same as those in Example 1. The differences are as follows:

[0120] In the modified powder added to the slag pot, the components and mass ratio are reducing agent: calcareous material: siliceous material: molten steel slag = 0.08:0.23:0.055:1; the particle diameters of each component are not greater than 40 mm (D50 = 35 mm);

[0121] The reducing agent is a mixture of activated carbon with a carbon content ≥ 89.5 wt% and solid carbon pitch, prepared according to a mass ratio of 1:1; the activated carbon is produced by Fuchen Tianjin Chemical Reagent Co., Ltd., and the carbon pitch is the solid carbon pitch produced by Hebei Deri New Material Technology.

[0122] The calcareous material is calcium oxide, and the content of calcium oxide is 99.95 wt%, which is produced by Shanghai Huake Experimental Equipment Co., Ltd.

[0123] The siliceous material is quartz sand, in which the content of silicon dioxide is 99.7 wt%, which is produced by Xi'an Yizhichen Biotechnology Co., Ltd.

[0124] In the preparation method of this example, the differences are as follows:

[0125] S2. Regulation of molten steel slag components under heat preservation

[0126] Keep the temperature of the steel slag in the slag pot in a molten state at 1500 - 1600 °C. After adding the pre-prepared modified powder to the molten steel slag, mix and stir. The stirring speed is 10 r / min, and the stirring time is 60 min;

[0127] S3. Phase modification and reconstruction in the heat preservation stage

[0128] After reaching the set stirring time, stop stirring and continue to keep the molten state of the steel slag in the slag pot at 1500-1600 °C for 30 minutes of heat preservation to homogenize the composition of the molten steel slag; after the heat preservation ends and the slag and iron are separated, recover the molten iron that naturally settles at the bottom of the slag pot and reuse it for steel production, and transfer the molten modified steel slag that naturally floats on the upper part of the slag pot to another heat-preserved slag pot for modification;

[0129] S4. Phase reconstruction of the first-stage cooling of modified steel slag

[0130] For the molten modified steel slag with a temperature of 1500-1600 °C after transfer, adopt the air-cooling method (natural cooling) and control the slow cooling of the modified steel slag to 1250-1300 °C at a rate of 10-30 °C / min for the first-stage cooling phase reconstruction. During this process, the main phases of cement clinker, 3CaO·SiO2 and 2CaO·SiO2, precipitate from the molten modified steel slag, and small crystals gradually grow and develop;

[0131] S5. Phase reconstruction of the second-stage cooling of modified steel slag

[0132] After the modified steel slag is slowly cooled to 1250-1300 °C, then adopt the air-cooling method and control the rapid cooling of the modified steel slag from 1250-1300 °C to room temperature at a cooling rate of 70 °C / s.

[0133] For other contents of the preparation method, materials and applications of this embodiment, they are the same as those of Embodiment 1. For the steel slag used and the performance of the prepared steel slag modified cementitious material, see the appendix Figure 1 The chemical composition of the prepared steel slag modified cementitious material is shown in Table 2, and the results of the iron reduction rate and the free calcium oxide content are shown in Table 1.

[0134] Embodiment 5

[0135] The steel slag modified cementitious material, preparation method and its application provided in this embodiment are also specific applications based on the foregoing basic embodiment. The basic contents of the preparation method, materials and applications of this embodiment are all the same as those of Embodiment 1, and the differences are as follows:

[0136] The components and mass ratio of the modified powder added to the slag pot are reducing agent: calcareous material: siliceous material: molten steel slag = 0.18:0.23:0.055:1; the particle diameters of each component are not more than 40 mm (D50 = 30 mm);

[0137] The reducing agent is a mixture of activated carbon with a carbon content ≥ 89.5 wt% and solid carbon pitch prepared according to a mass ratio of 1:1; the activated carbon is produced by Fuchen Tianjin Chemical Reagent Co., Ltd., and the carbon pitch is the solid carbon pitch produced by Hebei Deri New Material Technology.

[0138] The calcium material is calcium oxide, and the content of calcium oxide is 99.95 wt%, which is produced by Shanghai Huake Experimental Equipment Co., Ltd.

[0139] The silica material is quartz waste with a silica content of 99.5 wt%, which is the waste after the production of beakers by Shuniu Glass Instrument Co., Ltd.

[0140] In the preparation method of this embodiment, the differences are as follows:

[0141] S2. Regulation of molten steel slag components under heat preservation

[0142] Keep the temperature of the molten steel slag in the slag pot in a molten state at 1500 - 1600 °C. After adding the pre-prepared modified powder to the molten steel slag, mix and stir. The stirring speed is 50 r / min, and the stirring time is 10 min.

[0143] S3. Phase modification and reconstruction during the heat preservation stage

[0144] After reaching the set stirring time, stop stirring and continue to keep the temperature of the molten steel slag in the slag pot in a molten state at 1500 - 1600 °C for 50 min to make the composition of the molten steel slag uniform. After the heat preservation ends and after the slag and iron are separated, the molten iron that naturally settles at the bottom of the slag pot is recovered and reused for steel production. The molten modified steel slag that naturally floats on the upper part of the slag pot is transferred to another heat-preserved slag pot for modification.

[0145] S4. Phase reconstruction during the first-stage cooling of modified steel slag

[0146] For the molten modified steel slag with a temperature of 1500 - 1600 °C after transfer, use the air-cooling method (natural cooling) to control the slow cooling of the modified steel slag to 1250 - 1300 °C at a rate of 10 - 30 °C / min for the first-stage cooling phase reconstruction. During this process, the main phases of cement clinker, 3CaO·SiO2 and 2CaO·SiO2, precipitate from the molten modified steel slag, and small crystals gradually grow and develop.

[0147] S5. Phase reconstruction during the second-stage cooling of modified steel slag

[0148] After the modified steel slag is slowly cooled to 1250 - 1300 °C, then use the air-blast cooling method to control the rapid cooling of the modified steel slag from 1250 - 1300 °C to room temperature at a cooling rate of 70 °C / s.

[0149] For other contents of the preparation method, materials and applications in this embodiment, they are the same as those in Embodiment 1. The properties of the steel slag and the prepared steel slag modified cementitious material are shown in the appendix Figure 1 , and the chemical composition of the prepared steel slag modified cementitious material is shown in Table 2, and the results of the iron reduction rate and the free calcium oxide content are shown in Table 1.

[0150] In the above embodiments, the reduction rate of iron R Fe can be obtained from Formula 1:

[0151] Formula 1

[0152] where C 0 is the total iron content of the molten steel slag and the modified powder, C 1 is the total iron content of the modified molten steel slag.

[0153] The free calcium oxide content of the modified steel slag was determined according to the national standard method GB / T 176-2017 Cement Chemical Analysis Method.

[0154] The iron reduction rate and free calcium oxide content results of the modified steel slag in Examples 1 to 5 are shown in Table 1, and the chemical composition of the prepared steel slag modified cementitious material is shown in Table 2.

[0155] Table 1

[0156]

[0157] As can be seen from Table 1, the iron reduction rate in all examples of the present invention is greater than 97%, and basically all iron has been removed. Moreover, the free calcium oxide content is less than the requirement of ≤1.5% in the national standard GB / T 21372-2024 Portland cement clinker. It can be seen that the component contents in all examples meet the national standards.

[0158] Table 2

[0159]

[0160] As can be seen from Table 2, the iron content in the steel slag modified cementitious material is significantly reduced, and basically all has been reduced to elemental iron. Moreover, the component composition and crystal particle size and other phases all meet the requirements of the national standard GB / T 21372-2024 "Portland Cement Clinker", especially the requirements for the magnesium oxide content, sulfur trioxide content, calcium-silicon ratio, and silicate mineral content, enabling it to be directly used as the clinker of cement and applied to the manufacture of cement.

[0161] XRD tests were carried out on the original steel slag material and the steel slag modified cementitious materials prepared in Examples 1 to 5, and the results are as Figure 1 shown. From Figure 1It can be seen that the main phases in the original steel slag are dicalcium silicate (2CaO·SiO2, i.e., C2S), dicalcium ferrite (Ca2Fe2O5, i.e., C2F), and RO phase solid solution. During the modification process, the molten steel slag reacts with the modified powder, and after two-phase reconstructions, a steel slag modified cementitious material is obtained. At this time, its phase composition is tricalcium silicate (3CaO·SiO2, i.e., C3S), dicalcium silicate (2CaO·SiO2), tricalcium aluminate (3CaO·Al2O3, i.e., C3A), and magnesium oxide, which is basically the same as that of cement clinker. The backscattering test was carried out on the steel slag modified cementitious material prepared in Example 3, and the results are as Figure 2 shown. In the steel slag modified cementitious material, zonal or polygonal 3CaO·SiO2, elliptical and irregular 2CaO·SiO2, and 3CaO·Al2O3 are formed, which are similar to the micro-morphology of cement clinker. Among them, 3CaO·SiO2 and 2CaO·SiO2, which are the main minerals of portland cement clinker, are well-developed, with moderate crystal sizes and clear interfaces.

[0162] Comparative Example 1

[0163] The method for preparing portland cement clinker provided in this comparative example uses the same components (steel slag, modified powder), ratio, and main preparation process as in Example 3 described above. The difference is that it omits the first-stage cooling and phase reconstruction of the modified steel slag in step S4 and directly proceeds to step S5, where the modified steel slag at 1600 °C is directly quenched to room temperature at a cooling rate of 55 °C / s (air cooling method) to obtain a massive steel slag modified cementitious material, which is then ground into a powder for testing.

[0164] The schematic diagram of the XRD test of the powder of the steel slag modified cementitious material prepared in this comparative example is shown in the appendix Figure 3 . From Figure 3 this, it can be seen that in the modified material directly quenched from the molten state at 1500 - 1600 °C to room temperature, a large amount of 3CaO·SiO2 is not generated, but only 2CaO·SiO2 is generated. Its components, ratio, crystal particle size, etc. do not meet the standard requirements and cannot be used as portland cement clinker.

[0165] In summary, the above embodiments of the present invention provide a steel slag modified cementitious material, a preparation method and its application. Through the synchronous improvement of the formula and the preparation process, the molten steel slag is directly transported and modified by a slag ladle, and through a method of heat preservation and two-stage cooling for phase reconstruction and modification, the content of each component and the phase such as crystal growth in the steel slag are controlled, so that each component of the molten steel slag and the modified powder interact with each other and gradually form the main phases 3CaO·SiO2 and 2CaO·SiO2 contained in cement clinker. The phase composition such as the steel slag component and crystal grain size of the finally obtained modified cementitious material is simultaneously approximated to the phase of cement clinker. The content of each component in the powder steel slag modified cementitious material is controlled within the range required by the new national standard GB / T 21372-2024 for Portland cement clinker (including the content of free calcium oxide, etc.), so that the treated modified cementitious material can replace cement clinker, obtaining a cementitious material with high value and large consumption capacity. The cement products manufactured meet the requirements for common Portland cement in the GB 175-2023 standard, improving the resource utilization value and total consumption capacity of steel slag, and having high utilization value in industry.

[0166] Within the scope of the above components, ratios and processes described in the specification of the present invention, the steel slag modified cementitious material, the preparation method and its application obtained by making other specific selections can all achieve the technical effects described in the present invention, so they will not be listed one by one.

[0167] The above embodiments have described the present invention, but the content described is only the preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention shall fall within the protection scope of the present invention.

Claims

1. A preparation method of a steel slag modified cementitious material, characterized in that, It includes the following steps: S1. Collect high-temperature steel slag Use a heat-insulated intermediate slag ladle to collect the high-temperature molten steel slag discharged from the steelmaking converter and transport it to the modification treatment workshop; The steel slag is ordinary converter molten steel slag, and its total iron content is 20-40wt%; S2. Regulation of molten steel slag components under heat preservation Keep the temperature of the steel slag in the slag pot in a molten state at 1500~1600 °C. After adding the pre-prepared modified powder to the molten steel slag, mix and stir. During the stirring process, Ca 2+ ions diffuse and react with silicate ions and 2CaO·SiO2 to carry out phase reconstruction, forming the main phase 3CaO·SiO2 of portland cement. At the same time, the iron-containing phase in the molten steel slag reacts with the reducing agent in the modified powder to generate elemental iron; The modified powder is a mixed powder composed of a reducing agent, a calcareous material, and a siliceous material with a set ratio and a particle diameter of 5-50mm. The mass ratio of each component is reducing agent: calcareous material: siliceous material: molten steel slag = (0.08-0.18):(0.12-0.23):(0.018-0.055):1; S3. Phase modification and reconstruction during the heat preservation stage Stop stirring and continue to keep the temperature of the steel slag in the slag ladle in a molten state at 1500-1600°C for 30-60 minutes to make the composition of the molten steel slag uniform. During this process, the molten iron reduced settles naturally to the bottom of the slag ladle, and the regulated molten modified steel slag floats naturally on the upper part of the slag ladle; transfer the molten modified steel slag floating naturally on the upper part of the slag ladle to another heat-insulated slag ladle for modification to separate the slag from the iron; S4. Phase reconstruction during the first-stage cooling of the modified steel slag For the molten modified steel slag with a temperature of 1500-1600°C after transfer, control the slow cooling of the modified steel slag to 1250-1300°C at a rate of 10-30°C / min for the first-stage cooling phase reconstruction. During this process, the main phases of the cement clinker, 3CaO·SiO2 and 2CaO·SiO2, precipitate from the molten modified steel slag, and the small crystals gradually grow; S5. Phase reconstruction during the second-stage cooling of the modified steel slag Control the rapid cooling of the modified steel slag from 1250-1300°C to room temperature at a cooling rate of 40-70°C / s. This process stops the continuous growth of the formed 3CaO·SiO2 crystals, makes the 3CaO·SiO2 crystals moderate, inhibits the decomposition of the 3CaO·SiO2 phase, and prevents the polymorphic transformation of 2CaO·SiO2 into the γ form, enabling the components of the molten modified steel slag to interact with each other and gradually form the main phases contained in the cement clinker, 3CaO·SiO2 and 2CaO·SiO2; S6. Post-treatment after cooling Cool the product of step S5 to room temperature to obtain a blocky steel slag modified cementitious material that has undergone heat preservation and two-stage cooling phase reconstruction. First, crush it and then grind it to a specific surface area of 300m² / kg ≤ SSA ≤ 400m² / kg to prepare a portland cement clinker mainly composed of the phases 3CaO·SiO2 and 2CaO·SiO2.

2. The preparation method of the steel slag modified cementitious material according to claim 1, characterized in that, Step S3 also includes the following steps: S3-1. Recover the molten iron that has naturally settled to the bottom of the slag ladle in step S3 and reuse it for steel production.

3. The preparation method of the steel slag modified cementitious material according to claim 1, characterized in that, In step S2, when adding the modified powder to the slag ladle for mixing, stir at a speed of 10-50 r / min for 10-60 minutes.

4. The preparation method of the steel slag modified cementitious material according to claim 1, characterized in that, For the slow cooling in the first-stage cooling phase reconstruction of the modified steel slag in step S4, the air-cooling method is adopted; for the rapid cooling in the second-stage cooling phase reconstruction of the modified steel slag in step S5, the air-blowing method is adopted.

5. The preparation method of the steel slag modified cementitious material according to claim 1, characterized in that, The reducing agent is one or more of coke particles, activated carbon, carbon pitch, and recycled graphite products, and the carbon content is ≥ 85 wt%.

6. The preparation method of the steel slag modified cementitious material according to claim 1, characterized in that The calcium-containing material in the modified powder contains calcium oxide, and the content of calcium oxide is 90 - 100 wt%.

7. The preparation method of the steel slag modified cementitious material according to claim 1, characterized in that, The silicon-containing material in the modified powder is one or more of quartz sand, silica fume, and quartz waste, and the content of silicon dioxide is 90 - 100 wt%.

8. A steel slag modified cementitious material, characterized in that, It is prepared by the method according to any one of claims 1 - 7.

9. Application of the steel slag modified cementitious material according to claim 8 as a clinker in the preparation of ordinary Portland cement.

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