Supercritical carbon dioxide rapid dry carbonization of steel slag and its preparation method and application

Abstract

The present invention discloses a supercritical carbon dioxide rapid dry carbonization of steel slag and its preparation method and application. The steel slag particles are subjected to a crushing-iron selection-grinding process, and then ground to obtain steel slag powder, which is then dried. The steel slag powder is mixed with water and an admixture in parts by mass: 100 parts of steel slag powder, 0-2 parts of water, and 1-5 parts of admixture to obtain a steel slag mixture. Finally, the steel slag mixture is sent to a supercritical carbon dioxide reactor, and CO2 gas is introduced. Under the supercritical state of CO2, the steel slag powder and supercritical CO2 undergo a rapid carbonization reaction under dry conditions to obtain the product. The present invention is a dry carbonization process for steel slag with a moisture content of less than 2%. The process utilizes the supercritical state of CO2, i.e., the diffusion of CO2 under the gas-liquid critical state, and a "solid-phase reaction" with the steel slag to generate an activated carbonized product. The product does not require subsequent drying and grinding operations, and the process is simple and energy-saving.

Description

Technical Field

[0001] The present invention belongs to resource utilization of solid waste building materials, and specifically relates to a supercritical carbon dioxide rapid dry carbonization steel slag and a preparation method and application thereof. Background Art

[0002] In recent years, reducing carbon dioxide emissions has become a growing concern, with the cement industry being a major contributor. Replacing cement clinker with various auxiliary cementitious materials, such as steel slag, fly ash, and slag powder, is the most direct and effective way to reduce carbon dioxide emissions from cement production. Furthermore, the addition of high-quality admixtures to cement can also improve the performance of cement-based materials. Therefore, the exploration of new admixtures that can capture carbon dioxide and reuse it in the cement industry is becoming increasingly important.

[0003] Steel slag is an industrial byproduct produced during the steelmaking process, accounting for 15% to 20% of total steel production. my country's accumulated slag stockpiles exceed 1.1 billion tons, with a comprehensive utilization rate of less than 30%. Large quantities of slag are dumped in landfills or in open-air storage, not only consuming land resources but also severely impacting the natural environment and posing serious risks to human health due to its high alkalinity and leaching potential for harmful metals. Therefore, new technologies are urgently needed to recycle slag in an environmentally friendly and resource-efficient manner.

[0004] The main low-activity phase in steel slag is γ-dicalcium silicate, which has extremely low hydration activity. Calcium-containing minerals in steel slag, such as free CaO and calcium silicate, have high carbonization reaction activity in a CO2-rich environment. Steel slag after carbonization reaction can solve problems such as poor volume stability and low activity, making it a way to effectively utilize steel slag. Free CaO, free MgO, Ca(OH)2 and Mg(OH)2 in steel slag can undergo carbonization reaction to produce calcium carbonate or magnesium carbonate, and C3S, CaSiO3, β-C2S and γ-C2S are carbonized to produce amorphous SiO2. The carbonization reaction process of steel slag includes the dissolution of CO2 to produce CO3 2- , Ca in steel slag 2 + Mg 2+ Dissolution and precipitation of CO3 2- With Ca 2+ Mg 2+ The reaction produces carbonates and amorphous SiO2. Carbonization of steel slag forms a dense carbonized layer on its surface, giving it higher particle strength and making it suitable for use as a concrete aggregate. Furthermore, the carbonized slag powder possesses a certain degree of activity, allowing it to replace some cement as a mixing material and admixture.

[0005] Current literature research shows that the activity index of carbonized steel slag is only slightly improved, and its effect on enhancing the performance of cement-based materials is not significant. Patent publication number CN114538867A discloses a method for preparing cement-based materials using carbonized steel slag slurry. The method involves mixing steel slag and water in an open agitator at a solid-to-liquid ratio of 0.15 to 0.45 to obtain a slurry. The slurry is then heated, the temperature is controlled at 20 to 80°C during the stirring process, and carbon dioxide gas is introduced while maintaining high-speed stirring. The steel slag slurry is stirred for 40 to 120 minutes at a stirring speed of 800 to 1200 rpm / min, the carbon dioxide concentration is 10 to 99.99%, and the gas flow rate is 1 to 9 L / min to obtain a carbonized steel slag slurry. Due to the solid-to-liquid ratio in this technology, the treated carbonized steel slag slurry needs to be filtered, dried, and ground, which involves many steps, and the activity of the treated steel slag is not significantly improved.

[0006] Patent CN115466072A studies a construction material and preparation method for CO2-mineralized solid waste from the steel industry, limits the mass ratio of mineralizable solid waste to silico-aluminous solid waste, and enables solid waste products to achieve a certain compressive strength while increasing the carbon fixation rate, and no additional heating is required during the process, saving energy. Patent CN114538876A studies a method for preparing mine cementitious filling materials using industrial / mining solid waste to mineralize CO2, organically integrating CO2 mineralization storage with geological storage technology, and realizing the upgrading and transformation of metal mining under the dual-carbon strategy. Patent CN113636772B proposes a steel slag-based thermal insulation filler and its preparation method and application, using steel slag, a binder, a penetrant, a pore-forming agent, and a flux, mixing the raw materials evenly and molding them into spherical particles, sintering the spherical particles to obtain a thermal insulation filler precursor, and then treating the thermal insulation filler precursor with supercritical carbon dioxide to obtain a steel slag-based thermal insulation filler finished product. Patent CN116854445A discloses a system, method and product for preparing building materials by co-mineralizing carbon dioxide with steel slag. Steel slag powder, gypsum and cement are mixed in a back-mixing mixing bin to obtain a mixture. The mixture, whole tailings and water are then fed into a constant temperature mineralization reactor and reacted under supercritical CO2 conditions to obtain the building material.

[0007] Existing carbonized steel slag technologies have limited effects on enhancing slag activity. Therefore, a method is needed to significantly increase the activity of carbonized steel slag, promote hydration reactions, absorb the free calcium oxide and magnesium oxide components in the slag, improve slag stability, and promote the widespread and high-value application of steel slag in the building materials industry. Summary of the Invention

[0008] Purpose of the invention: The technical problem to be solved by the present invention is to address the deficiencies of the existing technology and provide a method for rapid dry carbonization of steel slag using supercritical carbon dioxide, which significantly improves the activity of steel slag, improves the problems of low gelling property and volume stability of steel slag, expands the application range of steel slag, and further improves the resource utilization rate of steel slag.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing steel slag by rapid dry carbonization using supercritical carbon dioxide comprises the following steps:

[0011] (1) crushing, iron separation, and grinding the steel slag particles to obtain steel slag powder, and drying the powder;

[0012] (2) mixing steel slag powder, water and admixture according to the weight ratio: 100 parts of steel slag powder, 0-2 parts of water, and 1-5 parts of admixture to obtain a steel slag mixture;

[0013] (3) The steel slag mixture in step (2) is sent to a supercritical carbon dioxide reactor, and CO2 gas is introduced. Under the supercritical state of CO2, the steel slag powder and supercritical CO2 are rapidly carbonized under dry conditions to obtain the product.

[0014] Furthermore, in step (1), the steel slag particles are any one or more of converter slag, open-hearth slag, electric furnace slag, and ladle refined slag.

[0015] Furthermore, in step (1), the steel slag particles are crushed by a roller press, and then the iron blocks in the steel slag particles are removed by magnetic separation using an iron remover. The steel slag particles are then sent to a ball mill for grinding to 200-500 mesh to obtain steel slag powder, which is then dried at 100-110°C for 4-10 hours.

[0016] Crushing and grinding steel slag particles involves simple steps, high processing efficiency, and ease of implementation. Furthermore, the smaller the particle size of the steel slag powder, the greater its surface area, which facilitates a full reaction with supercritical CO₂, resulting in a higher carbonization efficiency within a given timeframe. However, if the particle size is too small, grinding the steel slag powder increases energy consumption. In the present invention, the steel slag is preferably ground to a mesh size of 200-400.

[0017] Specifically, in step (2), the admixture is selected from any one of CaSO4·2H2O, Na2CO3, and NaHCO3.

[0018] The addition of admixtures can promote the reaction, stimulate the reactivity of steel slag, and improve the performance of carbonized steel slag. The role of the admixture is to adjust the crystal form of the steel slag carbonization product to calcite. The carbonization product is mainly anhydrous crystalline calcium carbonate, and there are three crystal forms: calcite, aragonite and quartz. Among them, calcite has rhombus and rhombohedral structures, usually cubic or spindle-shaped particles, and has the most stable crystal form. During the reaction of steel slag with supercritical CO2, the formation of carbonate products (calcite) is induced. Since the particle size of the carbonization product calcium carbonate is small, it covers the surface of calcium silicate, increases the specific surface area, provides more nucleation points for the growth of calcium silicate hydration products, and improves the activity of carbonized steel slag.

[0019] Preferably, in step (3), CO2 gas is introduced into the supercritical carbon dioxide reactor, the CO2 gas flow rate is controlled to be 1-9 L / min, the pressure is increased to 8-10 MPa (preferably 10 MPa), and the temperature is increased to 50-80°C (preferably 60°C) to put CO2 in a supercritical state.

[0020] This invention involves dry carbonization of steel slag, with a moisture content of less than 2%. This method utilizes the diffusion of CO2 in the supercritical state, i.e., the gas-liquid critical state, and a "solid-phase reaction" with the steel slag to produce an activated carbonized product. Unlike wet carbonization of steel slag, which involves the dissolution of CO2 in the slag and a "liquid-phase reaction" with the slag, dry carbonization of steel slag in a supercritical CO2 state directly utilizes the more favorable gas-liquid critical state of CO2, allowing for a "solid-phase reaction" with the slag. This results in a faster reaction speed, improved carbonization product morphology, and enhanced slag activity.

[0021] Preferably, the volume ratio of CO2 in the introduced CO2 gas is above 99%.

[0022] Preferably, under the supercritical CO2 state, the carbonization reaction of CO2 and the steel slag mixture in the reactor is carried out for 1 to 10 minutes, preferably 5 to 10 minutes.

[0023] Furthermore, in step (3), a CO2 circulation system is used to control the CO2 gas flow rate to 1 to 9 L / min. The CO2 gas is compressed by a compressor to obtain a pressurized gas pressurized to 8 to 10 MPa, which is then sent to a temperature controller for heating and heating to 50 to 80°C. Then, supercritical CO2 gas is obtained and sent to a constant temperature reactor to participate in the reaction; after the supercritical CO2 gas comes out of the reactor, it is depressurized, cooled and circulated.

[0024] The steel slag of the present invention reacts quickly with supercritical CO2 gas, the steel slag can be continuously carbonized and produced, and the output of carbonized steel slag per unit time is high.

[0025] CO2 gas circulates within the supercritical CO2 reactor, maintaining a constant amount of CO2 as it is consumed by the reaction between slag and CO2. Furthermore, CO2 can be recycled within the supercritical equipment, reducing CO2 losses and improving CO2 utilization efficiency. This recycling of CO2 reduces CO2 emissions, mitigates environmental impacts, promotes the practical application and dissemination of CO2 emission reduction technologies, and enhances the environmental benefits and sustainability of CO2 utilization technologies.

[0026] The carbonized steel slag sample obtained by the reaction is removed to obtain carbonized steel slag powder. The resulting carbonized steel slag does not require subsequent drying and grinding steps, simplifying the process. Because the steel slag is carbonized using a supercritical CO2 dry method, the moisture content is very low. During the "solid-phase reaction" between the steel slag and supercritical CO2, the steel slag does not agglomerate or clump, and the specific surface area does not change significantly. Therefore, the carbonized steel slag sample does not require further drying and grinding, simplifying the process and reducing production energy consumption.

[0027] Furthermore, the present invention also claims protection for the carbonized steel slag prepared by the above preparation method.

[0028] Furthermore, the use of the carbonized steel slag prepared by the present invention as an admixture to replace cement is also within the protection scope of the present invention.

[0029] Beneficial effects:

[0030] First, the present invention utilizes dry supercritical CO2 to carbonize steel slag, leveraging the gas-liquid criticality of the supercritical CO2 state to induce a "solid-phase reaction" with the steel slag powder. Supercritical CO2 fluid possesses both the diffusivity of a gas and the solubility of a liquid, enabling rapid penetration of the CO2 into the steel slag. The carbonization reaction between the supercritical CO2 and the steel slag is both rapid and highly efficient.

[0031] Although there are existing solutions for carbonizing steel slag using carbon dioxide, this is usually done using gaseous carbon dioxide, which is slow and takes a long time. The present invention uses supercritical carbon dioxide treatment, which can effectively increase the carbonization rate and greatly shorten the carbonization time. At the same time, due to its good permeability, supercritical carbon dioxide can also improve the carbonization efficiency of steel slag. The supercritical carbon dioxide fluid improves the microscopic morphology of the steel slag surface and activates some inert components in the steel slag to a certain extent, allowing them to participate in the hydration reaction.

[0032] At the same time, the present invention uses dry supercritical CO2 carbonization of steel slag, which has a very short carbonization reaction time of only 1 to 10 minutes, enabling continuous carbonization production of steel slag and a high output of carbonized steel slag per unit time. In addition, the dry supercritical CO2 carbonization process of steel slag has a very low moisture content, and the steel slag does not agglomerate or agglomerate, and the specific surface area does not change significantly. Therefore, the carbonized steel slag sample does not need to be dried or ground, which simplifies the process and helps reduce production energy consumption.

[0033] Second: This invention uses dry supercritical CO2 to carbonize steel slag, significantly increasing its hydration activity. Supercritical CO2 reacts with the calcium oxide, magnesium oxide, and calcium silicate phases in the steel slag to produce nano-calcium carbonate and amorphous silicon dioxide, thereby increasing the reactivity of the steel slag. The carbonization reaction equations (1-4) are as follows:

[0034] CaO(s)+CO2(s,g)→CaCO3(s) (1)

[0035] MgO(s)+CO2(s,g)→MgCO3(s) (2)

[0036] Ca2SiO4(s)+2CO2(s,g)→2CaCO3(s)+SiO2(s) (3)

[0037] Ca3Mg(SiO4)2(s)+4CO2(s,g)→3CaCO3(s)+ MgCO3(s)+ SiO2(s) (4)

[0038] The nano-calcium carbonate generated by the carbonization reaction can be filled into the pores and matrix of cement-based materials, increasing the density of the matrix and providing more nucleation sites for cement hydration, promoting the formation of hydration products (e.g., CSH), thereby increasing the compressive strength of the carbonized steel slag cement-based material. The carbonized steel slag of the present invention has a high activity index, which greatly improves the problem of low cementitious properties of the steel slag. The activity index of the carbonized steel slag cement mortar can be as high as 90% of that of PI42.5 cement mortar, which is a significant improvement compared to the activity index reported in existing literature.

[0039] Third: The present invention utilizes supercritical CO2 to carbonize the free calcium oxide and magnesium oxide components in the steel slag, which not only absorbs the expansion components such as free calcium oxide and magnesium oxide in the steel slag, but also improves the volume stability of the steel slag and promotes the safe application of steel slag in cement-based materials.

[0040] Fourth, the present invention utilizes supercritical CO2 to carbonize steel slag, producing highly active carbonized steel slag. This can be used in building materials, such as as a cement concrete admixture, in the preparation of carbonized steel slag cementitious materials, and in the production of carbonized steel slag products. This enhances the application prospects of steel slag in building materials and has broad practical applications. The present invention utilizes a supercritical CO2 carbonization process to prepare carbonized steel slag, which can utilize industrial solid waste steel slag resources and convert them into resource-based products that can replace cement, thereby achieving sustainable utilization of steel slag resources, reducing environmental pollution, and alleviating pressure on the ecological environment.

[0041] This invention promotes CO2 utilization. Each ton of steel slag can absorb 63 to 170 kg of carbon dioxide, realizing the resourceful utilization of carbon dioxide in the building materials sector. This not only alleviates the waste of land resources and ecological issues caused by the large-scale storage of steel slag, but also reduces CO2 emissions. Furthermore, steel slag can be used as an alternative to traditional cement in the preparation of concrete materials, thereby increasing the utilization rate of steel slag, promoting carbon neutrality and the resourceful utilization of solid waste, thereby promoting the development of green building materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0043] Figure 1 This is the XRD spectrum of the carbonized steel slag in Example 1 at a temperature of 60°C, pressures of 8, 9 and 10 MPa, a liquid-to-solid ratio of 0.02, and carbonization for 5 minutes in a supercritical CO2 drying kettle.

[0044] Figure 2 This is a bar chart of the compressive strength of the control group and the groups mixed with 30% carbonized steel slag under the carbonization conditions of Example 1.

[0045] Figure 3 The XRD patterns of the carbonized steel slag in Example 2 were obtained at temperatures of 50, 60, and 70°C, a pressure of 10 MPa, a liquid-to-solid ratio of 0.02, and carbonization for 5 minutes in a supercritical CO2 drying kettle.

[0046] Figure 4 This is a bar chart of the compressive strength of the control group and the groups mixed with 30% carbonized steel slag under the carbonization conditions of Example 2.

[0047] Figure 5 This is the XRD spectrum of the carbonized steel slag in Example 3 at a temperature of 60° C., a pressure of 10 MPa, a liquid-to-solid ratio of 0 to 0.12, and carbonization for 5 minutes in a supercritical CO2 drying kettle.

[0048] Figure 6This is a bar chart of the compressive strength of the control group and the groups mixed with 30% carbonized steel slag under the carbonization conditions of Example 3.

[0049] Figure 7 The XRD patterns of the carbonized steel slag in Example 4 were obtained by carbonizing for 1, 3, 5 and 10 min in a supercritical CO2 drying kettle at a temperature of 60°C, a pressure of 10 MPa and a liquid-to-solid ratio of 0.02.

[0050] Figure 8 This is a bar graph of the compressive strength of the control group and the steel slag mixed with 30% carbonized slag under the carbonization conditions of Example 4.

[0051] Figure 9 These are the scanning electron micrographs (a, b) of the uncarbonized steel slag powder of Example 5 and the scanning electron micrographs (c, d) of the carbonized steel slag sample under the carbonization conditions of Example 5. DETAILED DESCRIPTION

[0052] The present invention can be better understood with reference to the following examples.

[0053] Example 1

[0054] The steel slag used in this embodiment 1 is Maanshan Iron and Steel Co., Ltd. steel slag, the main chemical components of which are shown in Table 1. The water used is tap water, and the admixture used is NaHCO3.

[0055] Table 1 Chemical composition of Maanshan Iron and Steel slag used in Example 1 (wt.%)

[0056]

[0057]

[0058] This embodiment 1 includes the following steps:

[0059] (1) The steel slag particles are crushed, iron-selected, and ball-milled, and then ground to 200-500 mesh, preferably 200-400 mesh, to obtain steel slag powder. The steel slag powder is dried at 105° C. for 4-10 hours.

[0060] (2) mixing steel slag powder, water and admixture according to the mass fraction: 100 parts of steel slag powder, 2 parts of water, and 1 part of admixture (NaHCO3) to obtain a steel slag mixture;

[0061] (3) sending the steel slag mixture in step (2) to a supercritical carbon dioxide reactor, introducing CO2 gas with a volume ratio greater than 99% into the supercritical carbon dioxide reactor, controlling the CO2 gas flow rate to 1 to 9 L / min, increasing the pressure to 8, 9, and 10 MPa, respectively, and heating to 60° C. to make the CO2 in a supercritical state. In this state, the CO2 and the steel slag mixture are carbonized for 5 minutes to obtain a carbonized steel slag sample;

[0062] (4) The carbonized steel slag sample obtained in step (3) was dried at 105° C. for 6 hours, and then ground to 200-500 mesh, preferably 200-400 mesh, to obtain carbonized steel slag powder.

[0063] The carbonized steel slag is used to prepare building materials to replace part of the cement and measure the relevant properties. The steps include:

[0064] (1) The control group of cement mortar was prepared using 450g of ordinary Portland cement, 1350g of standard sand, and 225g of water. The test groups of cement mortar were prepared using 135g of uncarbonized steel slag powder and supercritical CO2 carbonized steel slag powder, 315g of ordinary Portland cement, 1350g of standard sand, and 225g of water, respectively.

[0065] (2) adding the mixture in step (1) into a cement mortar mixer and stirring in the mixer for 3 to 4 minutes;

[0066] (3) Pour the stirred slurry into the mold and vibrate it on a cement mortar vibrating table for 120 seconds. Place the mold in a standard curing box and cure it for 1 day before demoulding. Finally, perform standard curing at a temperature of 25±2°C and a relative humidity of 95%;

[0067] (4) Test the 3-day and 28-day compressive strength of the cement mortar test group and the control group.

[0068] The XRD pattern of carbonized steel slag in the supercritical CO2 drying reactor is as follows: the temperature is 60℃, the pressure is 8, 9 and 10MPa respectively, the liquid-solid ratio is 0.02, and the carbonization time is 5min. Figure 1 The compressive strength bar graphs of the control group and the groups mixed with 30% carbonized steel slag are shown in Figure 2 As shown in Figure 2, it can be seen that the strength of the supercritical CO2 carbonized steel slag experimental group is significantly improved compared to the uncarbonized steel slag group.

[0069] According to the activity index test method in GB / T51003-2014 "Technical Specifications for the Application of Mineral Admixtures", the 3d and 28d compressive strengths of the above-mentioned cement mortar control group and the cement mortar experimental group were measured respectively, and then the 3d and 28d activity indices of carbonized steel slag were calculated according to the following formula.

[0070]

[0071] Where: A—activity index of carbonized steel slag (%);

[0072] R t —Strength (MPa) of the cement mortar test group at the corresponding ages (3d and 28d);

[0073] R0—Strength (MPa) of cement mortar control group at corresponding ages (3d and 28d).

[0074] The tested mortars are carbonized steel slag cement mortar and uncarbonized steel slag cement mortar, and the comparison mortar is PI42.5 cement mortar.

[0075] Calculation shows that the activity of uncarbonized steel slag is only 64.54%, while the 28d activity indexes of carbonized steel slag powder are 87.85%, 90.15% and 90.41% respectively. Among them, the carbonized steel slag powder under a pressure of 10 MPa has the highest activity.

[0076] Example 2

[0077] The steel slag used in this Example 2 is Maanshan Iron and Steel Co., Ltd. steel slag, the main chemical components of which are shown in Table 2. The water used is tap water, and the admixture used is NaHCO3.

[0078] Table 2 Chemical composition of Maanshan Iron and Steel slag used in Example 2 (wt.%)

[0079]

[0080] This embodiment 2 includes the following steps:

[0081] (1) The steel slag particles are crushed, iron-selected, and ball-milled, and then ground to 200-500 mesh, preferably 200-400 mesh, to obtain steel slag powder. The steel slag powder is dried at 105° C. for 4-10 hours.

[0082] (2) mixing steel slag powder, water and admixture according to the mass fraction: 100 parts of steel slag powder, 2 parts of water, and 2 parts of admixture (NaHCO3) to obtain a steel slag mixture;

[0083] (3) sending the steel slag mixture in step (2) to a supercritical carbon dioxide reactor, introducing CO2 gas with a volume ratio greater than 99% into the supercritical carbon dioxide reactor, controlling the CO2 gas flow rate to 1 to 9 L / min, increasing the pressure to 10 MPa, and heating to 50, 60, and 70° C., respectively, so that the CO2 is in a supercritical state. In this state, the CO2 and the steel slag mixture are carbonized for 5 minutes to obtain a carbonized steel slag sample;

[0084] (4) The carbonized steel slag sample obtained in step (3) was dried at 105° C. for 6 hours, and then ground to 200-500 mesh, preferably 200-400 mesh, to obtain carbonized steel slag powder.

[0085] The carbonized steel slag is used to prepare building materials to replace part of the cement and measure the relevant properties. The steps include:

[0086] (1) A cement mortar control sample was prepared using 450 g of ordinary Portland cement, 1350 g of standard sand, and 225 g of water. A cement mortar test group was prepared using 135 g of uncarbonized steel slag powder and supercritical CO2 carbonized steel slag powder, 315 g of ordinary Portland cement, 1350 g of standard sand, and 225 g of water, respectively.

[0087] (2) adding the mixture in step (1) into a cement mortar mixer and stirring in the mixer for 3 to 4 minutes;

[0088] (3) Pour the stirred slurry into the mold and vibrate it on a cement mortar vibrating table for 120 seconds. Place the mold in a standard curing box and cure it for 1 day before demoulding. Finally, perform standard curing at a temperature of 25±2°C and a relative humidity of 95%;

[0089] (4) Test the 3-day and 28-day compressive strength of the cement mortar test group and the control group.

[0090] The XRD patterns of carbonized steel slag in the supercritical CO2 drying reactor are as follows: Figure 3 The compressive strength bar graphs of the control group and the groups mixed with 30% carbonized steel slag are shown in Figure 4 As shown in the figure, it can be seen that the strength of the supercritical CO2 carbonized steel slag experimental group is significantly improved compared to the uncarbonized steel slag group. The 28-day activities of the carbonized steel slag powder are 87.75%, 90.41% and 87.79%, respectively. Among them, the carbonized steel slag at 60°C has the highest activity.

[0091] Example 3

[0092] The steel slag used in this embodiment 3 is Maanshan Iron and Steel Co., Ltd. steel slag, the main chemical components of which are shown in Table 3. The water used is tap water, and the admixture used is NaHCO3.

[0093] Table 3 Chemical composition of Maanshan Iron and Steel slag used in Example 3 (wt.%)

[0094]

[0095] This embodiment 3 includes the following steps:

[0096] (1) The steel slag particles are crushed, iron-selected, and ball-milled, and then ground to 200-500 mesh, preferably 200-400 mesh, to obtain steel slag powder. The steel slag powder is dried at 105° C. for 4-10 hours.

[0097] (2) mixing steel slag powder, water and admixture according to the mass fractions: 100 parts of steel slag powder, 0-12 parts of water, and 5 parts of admixture (NaHCO3) to obtain a steel slag mixture;

[0098] (3) sending the steel slag mixture in step (2) to a supercritical carbon dioxide reactor, introducing CO2 gas with a volume ratio greater than 99% into the supercritical carbon dioxide reactor, controlling the CO2 gas flow rate to 1 to 9 L / min, increasing the pressure to 10 MPa, and heating to 60° C. to make the CO2 in a supercritical state. In this state, the CO2 and the steel slag mixture are carbonized for 5 minutes to obtain a carbonized steel slag sample;

[0099] (4) The carbonized steel slag sample obtained in step (3) was dried at 105° C. for 6 hours, and then ground to 200-500 mesh, preferably 200-400 mesh, to obtain carbonized steel slag powder.

[0100] The carbonized steel slag is used to prepare building materials to replace part of the cement and measure the relevant properties. The steps include:

[0101] (1) A cement mortar control sample was prepared using 450 g of ordinary Portland cement, 1350 g of standard sand, and 225 g of water. A cement mortar test group was prepared using 135 g of uncarbonized steel slag powder and supercritical CO2 carbonized steel slag powder, 315 g of ordinary Portland cement, 1350 g of standard sand, and 225 g of water, respectively.

[0102] (2) adding the mixture in step (1) into a cement mortar mixer and stirring in the mixer for 3 to 4 minutes;

[0103] (3) Pour the stirred slurry into the mold and vibrate it on a cement mortar vibrating table for 120 seconds. Place the mold in a standard curing box and cure it for 1 day before demoulding. Finally, perform standard curing at a temperature of 25±2°C and a relative humidity of 95%;

[0104] (4) Test the 3-day and 28-day compressive strength of the cement mortar test group and the control group.

[0105] The XRD pattern of carbonized steel slag in the supercritical CO2 drying kettle is as follows: the temperature is 60℃, the pressure is 10MPa, the liquid-solid ratio is 0-0.12, and the carbonization time is 5min. Figure 5 The compressive strength bar graphs of the control group and the groups mixed with 30% carbonized steel slag are shown in Figure 6It can be seen that the activity of steel slag by supercritical CO2 dry carbonization (solid-liquid ratio of 0, 0.02) is significantly higher than that by wet carbonization (solid-liquid ratio of 0.04, 0.08 and 0.12). The 28d activity index of steel slag powder by supercritical CO2 dry carbonization is 91.17% and 90.41%, while the activity index of steel slag powder by wet carbonization is 76.75%, 72.92% and 68.21%.

[0106] Example 4

[0107] The steel slag used in this embodiment 4 is Maanshan Iron and Steel Co., Ltd. steel slag, the main chemical components of which are shown in Table 4. The water used is tap water, and the admixture used is NaHCO3.

[0108] Table 4 Chemical composition of Maanshan Iron and Steel slag used in Example 4 (wt.%)

[0109]

[0110] This embodiment 4 includes the following steps:

[0111] (1) The steel slag particles are crushed, iron-separated, and ball-milled, and then ground to 200-500 mesh, preferably 200-400 mesh, to obtain steel slag powder. The steel slag powder is dried at 105° C. for 4-10 hours.

[0112] (2) mixing steel slag powder, water and admixture according to the mass fraction: 100 parts of steel slag powder, 2 parts of water, and 4 parts of admixture (NaHCO3) to obtain a steel slag mixture;

[0113] (3) sending the steel slag mixture in step (2) to a supercritical carbon dioxide reactor, introducing CO2 gas with a volume ratio greater than 99% into the supercritical carbon dioxide reactor, controlling the CO2 gas flow rate to be 1 to 9 L / min, increasing the pressure to 10 MPa, and heating to 50, 60, and 70° C., respectively, so that the CO2 is in a supercritical state. In this state, the CO2 and the steel slag mixture are carbonized for 1, 3, 5, and 10 minutes to obtain carbonized steel slag samples;

[0114] (4) The carbonized steel slag sample obtained in step (3) was dried at 105° C. for 6 hours, and then ground to 200-500 mesh, preferably 200-400 mesh, to obtain carbonized steel slag powder.

[0115] The carbonized steel slag is used to prepare building materials to replace part of the cement and measure the relevant properties. The steps include:

[0116] (1) A cement mortar control sample was prepared using 450 g of ordinary Portland cement, 1350 g of standard sand, and 225 g of water. A cement mortar test group was prepared using 135 g of uncarbonized steel slag powder and supercritical CO2 carbonized steel slag powder, 315 g of ordinary Portland cement, 1350 g of standard sand, and 225 g of water, respectively.

[0117] (2) adding the mixture in step (1) into a cement mortar mixer and stirring in the mixer for 3 to 4 minutes;

[0118] (3) Pour the stirred slurry into the mold and vibrate it on a cement mortar vibrating table for 120 seconds. Place the mold in a standard curing box and cure it for 1 day before demoulding. Finally, perform standard curing at a temperature of 25±2°C and a relative humidity of 95%;

[0119] (4) Test the 3-day and 28-day compressive strength of the cement mortar test group and the control group.

[0120] The XRD patterns of carbonized steel slag in the supercritical CO2 drying reactor are as follows: the temperature is 60℃, the pressure is 10MPa, the liquid-solid ratio is 0.02, and the carbonization time is 1, 3, 5 and 10min. Figure 7 The compressive strength bar graphs of the control group and the groups mixed with 30% carbonized steel slag are shown in Figure 8 Therefore, it can be seen that the strength of the supercritical CO2 carbonized steel slag group is significantly improved compared with the uncarbonized steel slag group, and the 28d activity index is 88.18%, 88.85%, 90.41% and 90.75 respectively. Among them, the carbonized steel slag is more active when the time is 5min and 10min.

[0121] Example 5

[0122] The steel slag used in this embodiment 5 is Maanshan Iron and Steel Co., Ltd. steel slag, the main chemical components of which are shown in Table 5. The water used is tap water, and the admixture used is NaHCO3.

[0123] Table 5 Chemical composition of Maanshan Iron and Steel slag used in Example 5 (wt.%)

[0124]

[0125] This embodiment 5 includes the following steps:

[0126] (1) Steel slag powder, water and admixture are mixed according to the mass fractions: 100 parts of steel slag powder, 2 parts of water, and 1 part of admixture (NaHCO3) to obtain a steel slag mixture;

[0127] (2) The steel slag mixture in step (1) is sent to a supercritical carbon dioxide drying kettle, CO2 gas is introduced into the supercritical carbon dioxide drying kettle, the CO2 gas flow rate is controlled to be 1 to 9 L / min, the pressure is increased to 10 MPa, the temperature is increased to 60°C, and the steel slag mixture is carbonized for 5 minutes under the supercritical state of CO2 gas to obtain a carbonized steel slag sample.

[0128] By comparing the SEM images of carbonized steel slag ( Figure 9 (c) and (d)) and uncarbonized steel slag scanning electron microscopy ( Figure 9 Comparison between (a) and (b) shows that due to the diffusivity of carbon dioxide fluid in the supercritical state, the calcium ions (Ca 2+ ) can easily react with carbon dioxide in a supercritical state to form nano-scale calcium carbonate. Figure 9 As can be seen in (c, d), the surface of the carbonized steel slag sample forms porous carbonization products, primarily calcium carbonate. The original surface structure of the steel slag is almost invisible, covered and encapsulated by a large amount of carbonization products. These products provide additional nucleation sites for the hydration of C3S, promoting cement hydration. The carbonization and hydration products fill the pores, making the microstructure of the specimen more compact and improving the early strength. This demonstrates that carbonizing steel slag with supercritical carbon dioxide can enhance its activity and effectively improve the volume stability issues caused by free calcium oxide and free magnesium oxide in the slag.

[0129] The present invention provides a method and approach for the rapid dry carbonization of steel slag using supercritical carbon dioxide, as well as its preparation and application. While there are numerous methods and approaches for implementing this technical solution, the aforementioned are merely preferred embodiments of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for preparing steel slag by rapid dry carbonization using supercritical carbon dioxide, characterized in that: The steps include: (1) Crushing, iron separation and grinding the steel slag particles to obtain steel slag powder, and drying; (2) Steel slag powder, water and admixture are mixed according to the following weight ratios: 100 parts of steel slag powder, 0-2 parts of water, and 1-5 parts of admixture, to obtain a steel slag mixture; the water content of the steel slag mixture is less than 2%; (3) The steel slag mixture from step (2) is sent to a supercritical carbon dioxide reactor, and CO2 gas is introduced. Under the supercritical state of CO2, the steel slag powder and supercritical CO2 are rapidly carbonized under dry conditions to obtain the product; In step (1), the steel slag particles are any one or more of converter slag, open-hearth slag, electric furnace slag, and ladle refining slag; In step (2), the admixture is selected from any one of Na2CO3 and NaHCO3; In step (3), CO2 gas is introduced into the supercritical carbon dioxide reactor, the CO2 gas flow rate is controlled to be 1-9 L / min, the pressure is increased to 8-10 MPa, and the temperature is increased to 50-80°C, so that the CO2 is in a supercritical state; Under the supercritical CO2 state, the CO2 in the reactor carbonizes with the steel slag mixture for 1 to 10 minutes.

2. The method for preparing supercritical carbon dioxide rapid dry carbonization of steel slag according to claim 1, characterized in that: In step (1), the steel slag particles are crushed by a roller press, and then the iron blocks in the steel slag particles are removed by magnetic separation using an iron remover. The steel slag particles are then sent to a ball mill for grinding to 200-500 mesh to obtain steel slag powder, which is then dried at 100-110°C for 4-10 hours.

3. The method for preparing supercritical carbon dioxide rapid dry carbonization of steel slag according to claim 1, characterized in that: The volume ratio of CO2 in the introduced CO2 gas is more than 99%.

4. The method for preparing supercritical carbon dioxide rapid dry carbonization of steel slag according to claim 1, characterized in that: In step (3), a CO2 circulation system is used to control the CO2 gas flow rate to 1~9L / min. The CO2 gas is compressed by a compressor to obtain pressurized gas at 8~10MPa and then sent to a temperature controller for heating and heating to 50~80℃. Then, supercritical CO2 gas is obtained and sent to a constant temperature reactor to participate in the reaction; after the supercritical CO2 gas comes out of the reactor, it is depressurized, cooled and circulated.

5. The carbonized steel slag prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the carbonized steel slag according to claim 5 as an admixture to replace cement.

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