High-quality steel slag aggregate, preparation method and application thereof

Abstract

The application relates to high-quality steel slag aggregate and a preparation method and application thereof, the method is a grading carbonization process, which comprises the following steps: (1) primary carbonization and reduction: taking molten steel slag in a state of 1300 DEG C-1500 DEG C as raw material, continuously introducing industrial waste gas into a hot steaming tank for carbonization in a water spraying cooling process for 8h-14h, meanwhile, making the diiron trioxide in the steel slag be reduced into iron single element and magnetite, and obtaining primary carbonized steel slag; the volume ratio of CO2 in the industrial waste gas is 20%-30%, and the volume ratio of CO is 30%-60%; (2) secondary carbonization: selecting the primary carbonized steel slag below 10mm in step (1) as aggregate, spraying the steel slag aggregate according to a preset spraying amount in a closed container, maintaining the pressure in the closed container as 0.3-0.5 Mpa, continuously introducing the same industrial waste gas into the closed container for secondary carbonization, and making the free calcium oxide content in the steel slag aggregate be lower than 3%; and magnetically selecting the high-quality steel slag aggregate after secondary carbonization. According to the method, the high-quality steel slag aggregate meeting the relevant technical requirements can be prepared within 24h, and is used for preparing asphalt concrete.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization, more particularly to a high-quality steel slag aggregate, a preparation method and application thereof. BACKGROUND

[0002] In the process of steelmaking, slagging agents are needed to remove the various oxides formed in the molten iron. The slagging agents react with these oxides to form molten slag, which is usually discharged from the steelmaking furnace in liquid or semi-liquid form and is converted into solid form after cooling, i.e., steel slag. As a byproduct of the steel industry, the annual discharge of steel slag in China is as high as 160 million tons, accounting for about 85% of the global steel slag production. However, the comprehensive utilization rate of steel slag has been less than 30% for a long time. The accumulation of a large amount of steel slag not only wastes land resources but also continuously pollutes the soil with heavy metals. Steel slag has good mechanical properties and low price, and in theory, it can provide high-quality cementitious materials and road aggregates for the construction and road industries. However, the volume stability of steel slag is poor, and it will expand in volume under the influence of water-rich environment and temperature, thereby restricting its application in road engineering. The summary of existing research by Gao Ying et al. in the article "Research Progress on Steel Slag Volume Expansion Behavior and Modification Methods" shows that the main reason for the poor volume stability of steel slag is the presence of free calcium oxide, periclase, and a high content of metallic iron and other expansion components in the steel slag. When these components undergo hydration or oxidation, the volume expansion of steel slag is inevitable, and the high content of free calcium oxide is the key reason.

[0003] Currently, the main solution to the poor stability of steel slag is to modify the steel slag. Steel slag modification measures include aging modification, reconstruction modification, and carbonation modification. Among them, cold slag aging modification is the most commonly used treatment method, but steel slag aging needs to be placed outdoors for more than 6 months, which has a long aging period and low efficiency. The conventional carbonation process mainly grinds the aged steel slag particles into steel slag powder or micro-powder before carbonation. Generally, high-concentration or pure CO2 is used for one-time carbonation treatment of steel slag powder, but the carbonation efficiency of steel slag powder is relatively low at normal temperature and pressure, and it often takes several days to complete the carbonation of steel slag powder, resulting in a long production cycle. Compared with steel slag powder or micro-powder, steel slag aggregate has a lower conventional carbonation efficiency and a longer required period.

[0004] The existing carbonization treatment of steel slag aggregate is mainly different for different application scenarios of carbonized steel slag. For example, in patent CN 116874204 A, 0.075-20 mm size coarse steel slag is first screened from steel slag, then carbonization treatment is carried out by wet capture of carbon dioxide in industrial waste gas in a pressurized environment, and the ground product is used to prepare cementitious materials; in CN 117534426 A, steel slag is first mixed with desulfurization gypsum, water and chelating agent to prepare slurry, and then molded into steel slag block blanks, and then carbonized by industrial waste gas. However, there is no method that can combine the preparation process of conventional steel slag aggregate to perform carbonization treatment and directly prepare high-quality steel slag aggregate for application in asphalt concrete. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application provides a high-quality steel slag aggregate and its preparation method and application, which aims to combine the carbonization treatment with the conventional steel slag aggregate preparation process. It is found that using high-temperature molten steel slag as raw material, adopting staged carbonization, first passing industrial waste gas at a high temperature of 1300-1500 DEG C to carry out primary carbonization and reduction, reducing free calcium oxide while reducing the iron trioxide in the steel slag to iron single element and iron trioxide by CO in the industrial waste gas, then screening particles below 10 mm for secondary carbonization to reduce the free calcium oxide content in the steel slag aggregate to below 3%, and magnetically selecting to directly obtain high-quality steel slag aggregate. This method can reduce the free calcium oxide content in un-aged steel slag to below 3% within 24 hours by combining the preparation process of conventional steel slag aggregate, and can realize the rapid preparation of high-quality steel slag aggregate, thereby solving the technical problems of high free calcium oxide content in conventional steel slag aggregate, long cycle and low efficiency of existing treatment methods.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, a method for rapidly preparing high-quality steel slag aggregate is provided, which adopts a staged carbonization process, specifically including the following steps:

[0007] (1) Primary carbonization and reduction: using 1300-1500 DEG C molten steel slag as raw material, continuously passing industrial waste gas into the hot steaming tank for carbonization during the water cooling process for 8-14 hours, while reducing the iron trioxide in the steel slag to iron single element and iron trioxide, to obtain primary carbonized steel slag; the CO2 volume fraction in the industrial waste gas is 20-30%, and the CO volume fraction is 30-60%;

[0008] (2) Secondary carbonization: selecting the primary carbonized steel slag below 10 mm in step (1) as aggregate, spraying the steel slag aggregate according to the preset spraying amount, maintaining the pressure in the closed container at 0.3-0.5 MPa, continuously passing the same industrial waste gas into the closed container for secondary carbonization, so that the free calcium oxide content in the steel slag aggregate is less than 3%; and magnetically selecting the high-quality steel slag aggregate after secondary carbonization.

[0009] Preferably, the method for rapidly preparing high-quality steel slag aggregate, wherein the industrial waste gas is continuously introduced into the autoclave in step (1) for carbonization for 10-12 hours to obtain first-stage carbonized steel slag.

[0010] Preferably, the method for rapidly preparing high-quality steel slag aggregate, wherein the volume fraction of CO2 in the industrial waste gas is 20%-25%, the volume fraction of CO is 35%-50%, and the industrial waste gas is continuously introduced into the autoclave in step (1) for carbonization for 10 hours to obtain first-stage carbonized steel slag.

[0011] Preferably, the method for rapidly preparing high-quality steel slag aggregate, wherein the preset spraying amount in step (2) is 5%-15% of the mass of the steel slag aggregate, and the secondary carbonization time is 1-12 hours.

[0012] Preferably, the method for rapidly preparing high-quality steel slag aggregate, wherein the preset spraying amount is 10%-15% of the mass of the steel slag aggregate, the pressure in the closed container in step (2) is maintained stable, and the same industrial waste gas is continuously introduced for carbonization for 6-9 hours.

[0013] Preferably, the method for rapidly preparing high-quality steel slag aggregate, wherein the pressure in the closed container in step (2) is maintained stable, and the industrial waste gas is continuously introduced for carbonization for 6 hours.

[0014] Preferably, the method for rapidly preparing high-quality steel slag aggregate, further comprising tertiary carbonization and / or quaternary carbonization, wherein the tertiary carbonization comprises spraying the steel slag aggregate after the secondary carbonization according to a preset spraying amount, maintaining the pressure in the closed container at 0.3-0.5 MPa, and continuously introducing the same industrial waste gas for carbonization for 3-6 hours to obtain tertiary carbonized steel slag aggregate.

[0015] The quaternary carbonization comprises spraying the steel slag aggregate after the tertiary carbonization according to a preset spraying amount, maintaining the pressure in the closed container at 0.3-0.5 MPa, and continuously introducing the same industrial waste gas for carbonization for 1-2 hours.

[0016] Preferably, the method for rapidly preparing high-quality steel slag aggregate, wherein the acid solution with a pH of 2-4 is used for spraying in the tertiary carbonization and / or the quaternary carbonization, the preset spraying amount is 10% of the mass of the steel slag aggregate, the pressure in the closed container is maintained at 0.3 MPa, the industrial waste gas is continuously introduced for carbonization for 3 hours in the tertiary carbonization, and the industrial waste gas is continuously introduced for carbonization for 1 hour in the quaternary carbonization.

[0017] According to another aspect of the present application, a high-quality steel slag aggregate is also provided, which is prepared according to the method described in the present application, has a free calcium oxide content of <3.0%, and has an apparent relative density of 3.2-3.3.

[0018] Preferably, the high-quality steel slag aggregate has a free calcium oxide content of 1.2% to 1.7% and an iron content of ≤1.1% in the steel slag aggregate.

[0019] According to another aspect of the present application, there is also provided use of the steel slag aggregate as described in the present application in preparation of asphalt concrete.

[0020] Overall, compared with the prior art, the above technical solutions conceived by the present application can achieve the following beneficial effects due to the use of molten steel slag as raw material and the adoption of the staged carbonization process:

[0021] The method for rapidly preparing high-quality steel slag aggregate provided by the present application uses molten steel slag at 1300-1500 DEG C as raw material, adopts industrial waste gas with a CO2 volume ratio of 20%-30% and a CO volume ratio of 30%-60% for staged carbonization, and simultaneously reduces ferroferric oxide in the steel slag to iron and magnetite using CO in the industrial waste gas during high-temperature first-stage carbonization; the first-stage carbonized steel slag is used as aggregate, and the same industrial waste gas is introduced for second-stage carbonization to make the free calcium oxide content in the steel slag less than 3%, and low-density high-quality steel slag aggregate is obtained through magnetic separation. The method can reduce the free calcium oxide content in un-aged steel slag to less than 3% within 24 hours in combination with the preparation process of conventional steel slag, realizes rapid and direct preparation of high-quality steel slag aggregate, and is used for preparation of asphalt concrete. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is an AC-10 asphalt mixture grading curve;

[0023] Figure 2 is the morphology of the steel slag before and after carbonization under an optical microscope;

[0024] Figure 3 is a comparison of the mechanical properties of the steel slag before and after carbonization. DETAILED DESCRIPTION

[0025] To further illustrate the technical means adopted by the present application to achieve the predetermined purposes and the effects, the specific embodiments, structures, features and effects according to the present application are described in detail below in combination with the drawings and preferred embodiments.

[0026] Steel slag is a byproduct of the steelmaking process, mainly generated by the reaction of molten iron and lime and other slagging materials under high temperature conditions. When the molten slag accumulates to a certain amount, it needs to be discharged from the furnace. The discharged molten slag is cooled to form solid conventional steel slag. The raw material of steel slag is crushed and screened to obtain steel slag aggregate of different particle sizes. The steel slag aggregate generally refers to the steel slag with a particle size of 0.075 mm to 10 mm. The particle size of the fine steel slag aggregate is 0.075 mm to 2.36 mm, and the coarse steel slag aggregate generally includes two grades, i.e., the steel slag aggregate with a particle size of 2.36 mm to 4.75 mm and the steel slag aggregate with a particle size of 4.75 mm to 10 mm. The particle size of the steel slag fine powder is generally microns. The existing carbonization process is mainly used for carbonization treatment of steel slag fine powder, which can reduce the free calcium oxide content to below 3%. However, it is difficult to achieve such a reduction in steel slag aggregate, mainly because the steel slag aggregate with a particle size of 1 mm or more has a small specific surface area and is difficult to directly absorb CO2 for carbonization.

[0027] In view of the characteristics of the existing steel slag aggregate that is difficult to be quickly carbonized, the present application explores a carbonization process suitable for steel slag aggregate to quickly reduce the free calcium oxide content in the steel slag aggregate. The inventors have found through a large number of experiments that using high-temperature molten steel slag as raw material and adopting a staged carbonization process can quickly reduce the free calcium oxide content in the steel slag aggregate to meet the technical requirements. The staged carbonization process includes primary carbonization and reduction, and secondary carbonization. The primary carbonization and reduction use 1300-1500℃ molten unaged steel slag as raw material, pour the raw material into a hot steaming tank, continuously introduce industrial waste gas for carbonization for 8-14 hours during the water spraying cooling process, and at the same time, reduce the iron trioxide in the steel slag to iron and magnetite with CO in the industrial waste gas to obtain primary carbonized steel slag. The CO2 volume fraction in the industrial waste gas is 20-30%, and the CO volume fraction is 30-60%. The secondary carbonization selects the primary carbonized steel slag with a particle size of 10 mm or less as aggregate, sprays the primary carbonized steel slag according to a preset spraying amount, places the sprayed primary carbonized steel slag aggregate in a sealed container, maintains the pressure in the sealed container at 0.3-0.5 MPa, and continuously introduces the same industrial waste gas for carbonization for 1-12 hours. The preset spraying amount is 5-15% of the mass of the steel slag aggregate. The high-quality steel slag aggregate after secondary carbonization, i.e., the secondary carbonized steel slag aggregate, is obtained by magnetic separation.

[0028] According to the method, high-quality steel slag aggregate with a free calcium oxide content of less than 3% and a lower density can be prepared within 24 hours, which meets the technical requirements of the transportation industry standard "Steel Slag for Asphalt Mixture" (JT / T 1086-2016) and can be applied to the preparation of asphalt concrete.

[0029] Based on this, the application provides a method for quickly preparing high-quality steel slag aggregate, which comprises the following steps:

[0030] (1) Primary carbonization and reduction: taking molten state unaged steel slag at 1300-1500 DEG C as raw material, pouring the raw material into a hot steamer, continuously introducing industrial waste gas into the hot steamer for carbonization for 8-14 hours in the process of water spraying cooling, at the same time, reducing Fe2O3 in the steel slag to elemental iron and Fe3O4 by CO in the industrial waste gas, and obtaining primary carbonized steel slag; the volume ratio of CO2 in the industrial waste gas is 20-30%, and the volume ratio of CO is 30-60%;

[0031] (2) Secondary carbonization: screening the primary carbonized steel slag obtained in step (1), selecting the primary carbonized steel slag below 10 mm as aggregate, spraying the primary carbonized steel slag according to a preset spraying amount, making free calcium oxide in the steel slag aggregate precipitate, placing the water-sprayed steel slag aggregate in a sealed container, maintaining the pressure in the sealed container at 0.3-0.5 MPa, continuously introducing the same industrial waste gas into the sealed container for secondary carbonization, and making the free calcium oxide content in the steel slag aggregate below 3%; and magnetically selecting the high-quality steel slag aggregate after secondary carbonization. The primary carbonized steel slag above 10 mm is washed and then conveyed to a roll crusher for re-crushing.

[0032] In step (1), CO in the industrial waste gas and non-magnetic Fe2O3 in the molten state steel slag generate elemental Fe and CO2 through a reduction reaction under high-temperature conditions of 900-1500 DEG C, and CO in the industrial waste gas and non-magnetic Fe2O3 in the molten state steel slag generate magnetic Fe3O4 and CO2 through a reduction reaction under specific conditions above 600 DEG C. The free calcium oxide in the molten state steel slag reacts with water vapor to generate calcium hydroxide, the temperature is reduced to below 600 DEG C, CO2 in the industrial waste gas reacts with the precipitated Ca 2+ reacts to generate stable CaCO3, thereby preliminarily carbonizing the molten state steel slag raw material. The reaction of the active components free calcium oxide and magnesium oxide in the steel slag with water causes the aggregate to expand to 1-2 times, accelerates the cracking of the large steel slag, finally the large aggregate becomes small aggregate, and more active components are exposed to continue to react with water, which is beneficial to improving the carbonization effect of the waste gas.

[0033] The reduction reaction in the first carbonization stage in the present application produces CO2 to supplement the amount of CO2 consumed in the hot leaching tank due to the carbonization reaction, which can promote the continuous progress of the carbonization reaction, while the carbonization reaction consumes the CO2 produced by the reduction reaction, which in turn also promotes the occurrence of the reduction reaction, forming more elemental iron and magnetic Fe3O4, which promote each other, can improve the stability of the steel slag while forming more elemental iron and magnetic Fe3O4, thereby improving the magnetism of the solid steel slag, which is beneficial to the magnetic separation of iron and magnetic Fe3O4 in the steel slag, thereby reducing the density of the steel slag, and also avoiding the waste of metallic iron oxides in the steel slag.

[0034] Preferably, the industrial waste gas is continuously introduced into the hot leaching tank in step (1) for carbonization for 10-12 h to obtain the first carbonized steel slag.

[0035] In some embodiments, the CO2 volume fraction in the industrial waste gas is 20%-25%, and the CO volume fraction is 35%-50%. The industrial waste gas is continuously introduced into the hot leaching tank in step (1) for carbonization for 10 h to obtain the first carbonized steel slag.

[0036] Preferably, the preset spraying amount is 5%-15% of the mass of the first carbonized steel slag aggregate, and the same industrial waste gas is continuously introduced into the closed container in step (2) for carbonization for 1-12 h to make the free calcium oxide content in the steel slag aggregate less than 3%, and the high-quality steel slag aggregate is obtained after magnetic separation after the second carbonization.

[0037] In some embodiments, during the second carbonization, pure water is sprayed, the preset spraying amount is 10-15% of the mass of the first carbonized steel slag aggregate, the pressure in the closed container in step (2) is maintained at 0.3-0.5 MPa, and the industrial waste gas is continuously introduced for carbonization for 3-9 h, preferably for 6-9 h, and more preferably for 6 h.

[0038] In some embodiments, during the second carbonization, pure water is sprayed, the preset spraying amount is 10% of the mass of the first carbonized steel slag, the pressure in the closed container is maintained at 0.3 MPa, and the industrial waste gas is continuously introduced for carbonization for 6 h.

[0039] Further, the method further comprises third carbonization and / or fourth carbonization, wherein the third carbonization is spraying the steel slag aggregate after the second carbonization according to a preset spraying amount, maintaining the pressure in the closed container at 0.3-0.5 MPa, and continuously introducing the same industrial waste gas for carbonization for 3-6 h to obtain the third carbonized steel slag aggregate;

[0040] The fourth carbonization is spraying the third carbonized steel slag aggregate according to a preset spraying amount, maintaining the pressure in the closed container at 0.3-0.5 MPa, and continuously introducing the same industrial waste gas for carbonization for 1-2 h.

[0041] In some embodiments, the tertiary carbonization or quaternary carbonization is carried out by spraying pure water or an acidic solution with a pH of 2-4, and the preset spraying amount is 10% of the mass of the steel slag aggregate. Preferably, in the tertiary carbonization, the pressure in the closed container is maintained at 0.3 MPa for 3 hours of carbonization by continuously introducing industrial waste gas; preferably, in the quaternary carbonization, the pressure in the closed container is maintained at 0.3 MPa for 1 hour of carbonization by continuously introducing industrial waste gas; more preferably, the spraying is carried out by using an acidic solution with a pH of 2-4.

[0042] In addition, the application also provides a high-quality steel slag aggregate, which is prepared according to the method of the application and has a free calcium oxide content of less than 3.0% and an apparent relative density of 3.2-3.3.

[0043] Preferably, the steel slag aggregate has a free calcium oxide content of 1.2-1.7% and an iron content of less than or equal to 1.1%.

[0044] According to another aspect of the application, the application also provides the use of the steel slag aggregate according to the application in the preparation of asphalt concrete.

[0045] The following is an example

[0046] Example 1: Graded carbonization of steel slag aggregate

[0047] In this example, hot molten slag from a steel plant is used as raw material to prepare high-quality steel slag aggregate, and the chemical composition of the steel slag is shown in the following table.

[0048] Table 1: Chemical composition of steel slag raw material

[0049] Composition MgO Al2O3 SiO2 P2O5 CaO MnO Fe2O3 TiO2 Other wt% 5.9 4.3 13.2 1.8 38.7 3.9 25.3 0.7 6.2

[0050] In the table, CaO includes inactive calcium oxide and active free calcium oxide (f-CaO), and f-CaO is a key factor affecting the stability of steel slag. The f-CaO content in unaged steel slag raw material is generally 5%-8% by weight, and the f-CaO content in the steel slag raw material detected in this example is 5.36%.

[0051] According to reports in Chinese Science and Nature: Chemical Engineering, a subjournal of the international top journal Nature, the main components of industrial waste gas are shown in Table 2.

[0052] Table 2: Composition of steel plant industrial waste gas

[0053] Gas source CO (%) CO2(%) [N2 (%)] [H2 (%)] CH4(%) Blast furnace gas 21-25 20-22 50-59 1-3 - Converter gas 39-48 20-22 20-30 1 - Coke oven gas 7-9 1-3 2-5 50-60 21-26

[0054] In this example, the industrial waste gas used is derived from steel converter gas, in which the volume fraction of CO2 is 20%-22% and the volume fraction of CO is 39%-48%. The molten steel slag is used as raw material for primary carbonization and reduction treatment, and the effects of industrial waste gas on steel slag carbonization under different carbonization conditions are compared, as follows:

[0055] (1) Different carbonization times on the effect of primary carbonization of molten steel slag

[0056] Primary carbonization and reduction: Pour 1300-1500℃ molten steel slag raw materials into a hot steamer, continuously sprinkle water on the surface of the molten steel slag raw materials, and introduce industrial waste gas into it for primary carbonization and reduction, compare the effects of different carbonization conditions on the carbonization of steel slag, as follows.

[0057] Table 3 Effect of different carbonization times on the f-CaO content of steel slag coarse aggregate

[0058]

[0059]

[0060] From the results in Table 3, with the extension of the primary carbonization time, the f-CaO content of the steel slag showed a trend of first decreasing and then tending to be stable. After 8h of primary carbonization, the f-CaO content of the steel slag decreased from 5.36% to 3.61%, a decrease of 32.65%, but with the extension of the carbonization time, the f-CaO content of the steel slag did not change significantly. However, during the primary carbonization process, the temperature in the hot steamer decreased with time, and the steel slag changed from molten state to solid state, which was easy to form large pieces of solid steel slag. In order to fully break down the large pieces of solid steel slag (to avoid difficulty in breaking down later), the carbonization time is usually extended for several hours, i.e. the preferred primary carbonization time is 10-12h, and more preferably the primary carbonization time is 10h.

[0061] From the above results, even if the primary carbonization time is extended, the f-CaO content of the steel slag aggregate remains basically at 3.5-3.6%, which is difficult to reduce further, and does not meet the technical requirements of the transportation industry standard "Steel Slag for Asphalt Mixture" (JT / T 1086-2016): f-CaO of steel slag ≤3%. It can be seen that for steel slag aggregate, primary carbonization is difficult to make its f-CaO content meet the relevant technical requirements.

[0062] Although the free calcium oxide content of the steel slag after the first carbonization is higher than 3%, the heat generated during the production of the steel slag (the temperature of the molten steel slag can reach 1300-1500°C) can be fully utilized during the first carbonization process. At a high temperature of 600°C or above, the ferric oxide in the steel slag can be reduced by CO, i.e., the non-magnetic ferric oxide in the steel slag is reduced to magnetic iron single element and magnetite by CO in the industrial waste gas during the first carbonization process. The iron single element and magnetite are screened out by magnetic separation, which not only can reduce the density of the steel slag aggregate after carbonization, thereby reducing the transportation cost of the steel slag, but also can reduce the amount of asphalt required for preparing asphalt concrete, avoid the waste of iron resources in the steel slag, and reduce the emission of CO and CO2 in the industrial waste gas.

[0063] (2) Effect of different pressures on the second carbonization

[0064] Further, based on the first carbonized steel slag aggregate obtained after the first carbonization for 14 hours, the effect of different pressures on the second carbonization of the steel slag aggregate was studied, as follows:

[0065] The first carbonized steel slag aggregate with a size of less than 10 mm was selected, and after being sprayed according to the preset spraying amount, it was placed in a sealed container and subjected to the second carbonization by introducing the same industrial waste gas, wherein the pressure in the sealed container was maintained at a set value (0.1 Mpa, 0.3 Mpa, or 0.5 Mpa) by introducing the industrial waste gas. The effect of different carbonization conditions on the f-CaO content in the steel slag aggregate was determined, and the results are as follows:

[0066] Table 4 Change in f-CaO content of steel slag aggregate under different carbonization conditions

[0067]

[0068]

[0069] From the determination results in Table 4, it can be seen that under the condition of the same preset spraying amount, the carbonization effect of the steel slag aggregate is better under a pressure of 0.3-0.5 Mpa, and the graded carbonization is preferably performed under a pressure of 0.3 Mpa.

[0070] (2) Effect of spraying amount and carbonization time on the graded carbonization of steel slag aggregate

[0071] The 150mm ground screen is used to screen the first carbonized steel slag, and the steel slag particles with a particle size of 150mm or less are used as standard materials. The steel slag aggregate with a particle size of 10mm or less is selected from the standard materials (the steel slag aggregate with a particle size of more than 10mm is washed and conveyed to a roll crusher by a conveyor belt for re-breaking to select the steel slag aggregate with a particle size of 10mm or less). The steel slag aggregate with a particle size of 10mm or less is subjected to graded carbonization treatment under the condition that the carbonization pressure is 0.3Mpa. The effects of water spraying amount and carbonization time on the carbonization effect of the steel slag are studied, and the optimal carbonization process is determined as follows:

[0072] Table 5 Effects of spraying amount and carbonization time on the secondary carbonization effect of the steel slag aggregate

[0073]

[0074]

[0075]

[0076] According to the determination results in Table 5, when the preset spraying amount is 10% to 15% of the mass of the steel slag aggregate, the secondary carbonization time is greater than or equal to 1h, or when the preset spraying amount is 5% of the mass of the steel slag aggregate, the secondary carbonization time is greater than or equal to 3h, the free calcium oxide content of the steel slag aggregate after secondary carbonization is less than 3.0%, which meets the technical requirements in the transportation industry standard “Steel Slag for Asphalt Mixture” (JT / T 1086-2016).

[0077] Under the condition that the water spraying amount is the same, with the prolongation of the carbonization time, the free calcium oxide content of the steel slag tends to decrease first and then stabilize. Increasing the spraying amount is beneficial to improving the carbonization effect. Considering comprehensively, the optimal secondary carbonization condition is that the preset spraying amount is 10%, the industrial waste gas is introduced to make the pressure in the sealed container reach 0.3Mpa, and the pressure is maintained for 6 to 9h. Under this carbonization condition, the free calcium oxide content of the steel slag can be reduced to about 2.10%, which is reduced by more than 41% compared with the first carbonized steel slag. The optimal secondary carbonization time is 6h.

[0078] After the secondary carbonization, the steel slag is subjected to magnetic separation by a magnetic separation device to separate out iron and other metals, and obtain elemental iron and steel slag aggregate with a particle size of 10mm or less. The apparent relative density of the steel slag aggregate after the secondary carbonization of the steel slag is about 3.3, and the apparent density of the untreated steel slag aggregate is 3.5. By using the method for carbonization treatment of the steel slag raw material, the time required for carbonization of the steel slag aggregate with a free calcium oxide content of less than or equal to 3% can be significantly shortened, the rapid and efficient carbonization treatment can be realized, and the density of the carbonized steel slag can be reduced.

[0079] Further, on the basis of the secondary carbonized steel slag aggregate obtained by secondary carbonization for 12 h at a preset spraying amount of 5%, 10%, and 15%, tertiary carbonization was performed to study the influence of the carbonization conditions of the tertiary carbonization on the carbonization effect of the steel slag aggregate, as follows:

[0080] The secondary carbonized steel slag aggregate below 10 mm (the steel slag aggregate above 10 mm was crushed, and the content of acicular and flaky steel slag aggregate after crushing was required to be not higher than 15%) was screened. The selected secondary carbonized steel slag aggregate below 10 mm was placed in a sealed container, and the same industrial waste gas was continuously introduced to compare the influence of different spraying amounts of pure water and carbonization time on the carbonization effect of the steel slag aggregate, as follows:

[0081] Table 6 Influence of spraying amount and carbonization time on the carbonization effect of the steel slag aggregate

[0082]

[0083]

[0084] The secondary carbonized steel slag aggregate was uniformly watered according to the preset spraying amount, and the surface of the steel slag was kept wet. The watered secondary carbonized steel slag aggregate was placed in a sealed container, and the same industrial waste gas was continuously introduced for carbonization. As can be seen from the measured results in Table 6, the preset spraying amount of pure water was 10% to 15% of the mass of the secondary carbonized steel slag aggregate, and the content of free calcium oxide in the steel slag aggregate could be reduced to below 2% after carbonization for more than 3 h. It is preferred that the preset spraying amount of the tertiary carbonization is 10%, and the carbonization time is 3 h.

[0085] Further, on the basis of the tertiary carbonized steel slag obtained by tertiary carbonization for 12 h at a preset spraying amount of 5%, 10%, and 15%, quaternary carbonization was performed to study the influence of the carbonization conditions of the quaternary carbonization on the carbonization effect of the steel slag aggregate, as follows:

[0086] The tertiary carbonized steel slag aggregate was subjected to magnetic separation, and the steel slag aggregate after magnetic separation was crushed. The content of acicular and flaky steel slag aggregate after crushing was required to be not higher than 15%. The crushed tertiary carbonized steel slag aggregate was placed in a sealed container, and the same industrial waste gas was continuously introduced to compare the influence of different spraying amounts and carbonization time on the carbonization effect of the steel slag aggregate, as follows:

[0087] Table 7 Influence of spraying amount and carbonization time on the carbonization effect of the steel slag aggregate

[0088]

[0089]

[0090]

[0091] From the results of Table 7, it can be seen that the carbonation effect of steel slag aggregate is not significantly improved with the extension of carbonation time in the fourth carbonation stage. When the preset spraying amount is 10%-15% and the carbonation time is 1 h, the overall carbonation effect is better. If the carbonation time is further extended, the carbonation effect of steel slag aggregate is not significantly improved. In summary, the fourth carbonation is preferably selected with a preset spraying amount of 10% and a carbonation time of 1 h, and the overall carbonation effect is better with a short carbonation cycle.

[0092] Preparation of high-quality steel slag aggregate in Example 2

[0093] High-quality steel slag aggregate was prepared by four-stage carbonation treatment using hot-state molten slag in the steelmaking process as raw material and converter gas as industrial waste gas. Solid waste steel slag was treated by hot stewing method and cooled, and pure CO2 was used for carbonation treatment as a control. The details are as follows:

[0094] First-stage carbonation and reduction: using 1300-1500℃ molten steel slag as raw material, the raw material was poured into a hot pot, water was continuously sprayed on the surface of the raw material, and industrial waste gas (converter gas) generated by converter steelmaking was introduced into the hot pot for carbonation for 10 h, so that the industrial waste gas and the steel slag were in full contact, the free calcium oxide in the steel slag reacted with water vapor, CO2 and CO in the industrial waste gas to form calcium carbonate, and the non-magnetic Fe2O3 in the steel slag was reduced to elemental Fe and Fe3O4, and first-stage carbonized steel slag was obtained.

[0095] 150mm floor screen screening: the first-stage carbonized steel slag was screened by 150mm floor screen, and the steel slag particles with a particle size of 150mm or less were used as qualified materials, and the unqualified materials were remelted and reused. The above operation was repeated until the qualified materials were obtained.

[0096] First-stage vibration screening: the first-stage carbonized steel slag with a particle size of 10mm or less was screened from the qualified materials as aggregate, and the first-stage carbonized steel slag aggregate with a particle size of more than 10mm was washed and conveyed to a roll crusher for re-crushing, and the first-stage carbonized steel slag aggregate with a particle size of 10mm or less was screened by second-stage vibration screening.

[0097] First-stage water spraying: the steel slag aggregate was uniformly sprayed with water at a rate of 10% of the mass of the steel slag aggregate, so that the surface of the steel slag was kept wet, the free calcium oxide in the steel slag could continue to precipitate outward, and the second-stage carbonation effect was improved.

[0098] Second-stage carbonation: the water-sprayed steel slag aggregate was placed in a sealed container, the pressure in the sealed container was maintained at 0.3Mpa, and the same industrial waste gas was continuously introduced for carbonation for 6h, so as to further reduce the content of free calcium oxide in the steel slag aggregate.

[0099] First magnetic separation: the second carbonized steel slag aggregate is subjected to first magnetic separation by a magnetic separation device to separate out iron and other metals, thereby obtaining elemental iron and second carbonized steel slag aggregate with iron content of less than or equal to 1.1% and a size of less than or equal to 10 mm.

[0100] Third carbonization: the second carbonized steel slag aggregate is subjected to crushing by a pair of rollers to obtain third carbonized steel slag aggregate with a needle-like content of less than or equal to 15%. The second carbonized steel slag aggregate is placed in a sealed container, and the pressure in the container is maintained at 0.3 MPa. The same industrial waste gas is continuously introduced into the container for carbonization for 3 hours to further reduce the free calcium oxide content of the steel slag aggregate.

[0101] Second magnetic separation: the third carbonized steel slag aggregate is subjected to second magnetic separation by a magnetic separation device to obtain elemental iron and low-density third carbonized steel slag aggregate. The apparent relative density of the steel slag aggregate after the magnetic separation is 3.2, which is lighter than the untreated steel slag aggregate with an apparent relative density of 3.5. This is conducive to reducing the transportation cost of the steel slag aggregate and reducing the actual amount of asphalt used.

[0102] Fourth carbonization: the third carbonized steel slag aggregate after the second magnetic separation is subjected to crushing by a cone crusher to obtain fourth carbonized steel slag aggregate with a needle-like content of less than or equal to 15%. The third carbonized steel slag aggregate is placed in a sealed container, and the pressure in the container is maintained at 0.3 MPa. The same industrial waste gas is continuously introduced into the container for carbonization for 1 hour to obtain fourth carbonized steel slag aggregate.

[0103] Third magnetic separation: the fourth carbonized steel slag aggregate is subjected to third magnetic separation by a magnetic separation device to obtain elemental iron and further reduce the density of the steel slag aggregate.

[0104] Second vibration screening: steel slag aggregate with a size of less than or equal to 4.75 mm is selected, and steel slag aggregate with a size of more than 4.75 mm is washed and then conveyed to a pair of rollers for crushing.

[0105] Third vibration screening: the washed and crushed steel slag aggregate is screened to obtain steel slag powder with a size of less than or equal to 0.075 mm, steel slag fine aggregate with a size of 0.075 mm to 2.36 mm (0.075 mm to 3 mm in construction), steel slag coarse aggregate with a size of 2.36 mm to 4.75 mm (3 mm to 5 mm in construction), and steel slag coarse aggregate with a size of 4.75 mm to 10 mm (5 mm to 10 mm in construction).

[0106] The first vibration screening is first vibration single-layer vibration. The vibration screen angle is 15° to 25°, the double amplitude is 8 mm, the vibration frequency is 870 Hz to 970 Hz, and the screen hole diameter is 10 mm or 11 mm.

[0107] The above-mentioned second-stage vibration screening is a second-stage vibration single-layer vibration, the vibration screen angle is 15°-25°, the double amplitude is 8 mm, the vibration frequency is 870 Hz and 970 Hz, and the screen hole diameter is 4.75 mm or 6 mm.

[0108] The above-mentioned third-stage vibration screening is a third-stage vibration single-layer vibration, the vibration screen angle is 15°-25°, the double amplitude is 8 mm, the vibration frequency is 870 Hz and 970 Hz, and the screen hole diameter is 4.75 mm, 2.36 mm and 0.075 mm.

[0109] The above-mentioned conveying belt is connected by a belt conveyor, and the belt speed range of the belt conveyor is set to 0.8-1.2 m / s. At the same time, considering the influence of aggregate particle size on conveying, the specific conveying rate is recommended as follows: the rate of the first-stage vibration screening-second-stage carbonization tank is 0.8 m / s, the rate of the first-stage magnetic separation-roller crusher is 0.8 m / s, the rate of the roller crusher-third-stage carbonization tank is 1.0 m / s, the rate of the second-stage magnetic separation-cone crusher is 1.0 m / s, the rate of the cone crusher-fourth-stage carbonization tank is 1.0 m / s, the rate of the third-stage magnetic separation-second-stage vibration screening is 0.8 m / s, and the rate of the third-stage vibration screening-discharge is 1.2 m / s.

[0110] A steel slag aggregate with an hourly output of 100 tons in a production line was detected to measure the performance indicators of the steel slag aggregate prepared in the embodiment and the aggregate prepared by the original process, respectively. According to the requirements of T304-2005, the corresponding improved and unimproved steel slag mixtures were prepared according to the AC-10 asphalt mixture gradation as shown in Figure 1 The expansion test was performed on the improved and unimproved steel slag mixtures according to the following specific steps:

[0111] According to the AC-10 asphalt mixture gradation curve as shown in Figure 1 The improved and unimproved steel slag mixtures were prepared according to the AC-10 asphalt mixture gradation curve, and the steel slag mixtures were placed in a constant-temperature water tank at 80°C for 7 days. The expansion rate of the steel slag aggregate before and after improvement was calculated according to the expansion rate formula: The average value of 3 tests after 7 days of heat preservation was taken as the final result. According to the proportion of coarse aggregate in the field construction, which is generally more than 60%, the expansion rate is recorded in the detection table of the coarse aggregate, and the results are shown in Table 8.

[0112] In the above formula, C1 is the expansion rate of the steel slag aggregate, D i is the aggregate expansion rate reading on the i-th day, and D0 is the initial expansion rate reading of the aggregate placed in the constant-temperature water tank.

[0113] In addition, the best water content of the carbonized steel slag mixture was obtained by test according to the requirements of T304-2005, and the results are shown in the following table.

[0114] Table 8 Technical test results of steel slag coarse aggregate before and after improvement

[0115]

[0116]

[0117] Table 9 Technical test results of steel slag fine aggregate before and after improvement

[0118]

[0119] The original process (control group) in Tables 8 and 9 is the metallurgical slag solid waste (steel slag) obtained by treating the hot-state molten slag in the steelmaking process by the hot stewing process and cooling, which is used as raw material for four-stage carbonization, wherein the steel slag particles are sprayed with water for wetting, sent into the carbonization chamber, the chamber door is closed, pure CO2 gas is introduced to make the CO2 partial pressure reach 0.2 MPa (referring to the carbonization conditions in Example 2 of CN110642545 A), and the carbonization time of each stage is the same as that in Example 2 above.

[0120] As can be seen from the test results in Tables 8 and 9, the performance indicators of the steel slag aggregate prepared according to the method meet the technical requirements in the industry standard “Steel Slag for Asphalt Mixture” (JT / T 1086-2016) of the transportation industry, and can be used as aggregate for preparing asphalt mixture. Compared with the steel slag aggregate prepared according to the original process, the free calcium oxide content of the steel slag aggregate prepared according to the method is significantly reduced, the water immersion expansion rate is as low as 0.3%, the stability of the steel slag aggregate is better, and the quality is more excellent.

[0121] Example 3 Optimization of Steel Slag Aggregate Graded Carbonization

[0122] In this example, acidic industrial waste liquid is added to pure water to prepare an acidic solution with a pH of 2-4 to replace the pure water in Example 2, and is sprayed at a preset spraying amount of 10% of the mass of the steel slag aggregate. Converter gas is used for carbonization treatment to explore the effect of steel slag aggregate graded carbonization, which is as follows:

[0123] Table 10 Effect of acidic solution on steel slag aggregate graded carbonization

[0124]

[0125]

[0126] As can be seen from the test results in Table 10, compared with spraying pure water, the steel slag aggregate sprayed with acidic solution has better effect on graded carbonization treatment using the same industrial waste gas, especially after the third-stage carbonization and the fourth-stage carbonization using acidic solution spraying treatment, the free calcium oxide content is lower, and the stability of the obtained steel slag aggregate is better.

[0127] Example 4 Performance change of steel slag before and after carbonization

[0128] (1) Steel slag morphology changes before and after carbonization

[0129] According to the construction requirements, fresh uncarbonized steel slag fine aggregate (particle size 0.075-3 mm) and coarse aggregate (3-5 mm), uncarbonized steel slag coarse aggregate (5-10 mm) placed outdoors for 1 month, and steel slag aggregate after secondary carbonization treatment according to Example 2 were selected as observation objects, and optical microscopy was used to observe whether the surface of the steel slag aggregate changed before and after carbonization, as follows:

[0130] The steel slag aggregate was washed with tap water, then placed in a 60°C oven for 3 h to ensure the dryness of the steel slag aggregate; the dried steel slag aggregate was placed under an optical microscope to observe the surface morphology of each group of steel slag aggregate, and the results are shown in Figure 2 .

[0131] Figure 2 (a) is uncarbonized steel slag fine aggregate (particle size 0.075-3 mm), (b) is steel slag fine aggregate (particle size 0.075-3 mm) after secondary carbonization treatment according to Example 2, (c) is uncarbonized steel slag coarse aggregate (particle size 3-5 mm), (d) is steel slag coarse aggregate (particle size 3-5 mm) after secondary carbonization treatment according to Example 2, (e) is uncarbonized steel slag coarse aggregate (particle size 5-10 mm) placed outdoors for 1 month, and (f) is steel slag coarse aggregate (particle size 5-10 mm) after secondary carbonization treatment according to Example 2.

[0132] From the observed surface morphology of the steel slag aggregate, Figure 2 it can be seen that white crystals (CaCO3) gradually appeared on the surface of the carbonized steel slag, and the surface color changed from brown-green to white. During the carbonization process, the steel slag reacted with CO2 in industrial waste gas to form CaCO3, changing the surface morphology of the steel slag. The surface of the uncarbonized steel slag aggregate was smooth, and the overall color was brown-green.

[0133] (2) Changes in mechanical properties of steel slag before and after carbonization

[0134] The mixture was compounded according to the AC-10 gradation, and then 3000 g of mixture above 2.36 mm was sieved out using a 2.36 mm sieve for testing. The improved crushing value test was used to detect the mechanical properties of the steel slag aggregate before and after carbonization, as follows:

[0135] According to the requirements of the "Specifications for Aggregate Testing in Highway Engineering" JTG E42-2005, four groups of 3000g steel slag (blended according to AC-10 gradation) were weighed and placed into a mold, recorded as m0. Subsequently, tests were conducted with loads of 200kN, 400kN, 600kN, and 800kN respectively. The crushed steel slag was passed through a 2.36mm sieve, and the mass of the sieved steel slag was recorded as m1. Each group was repeated three times, according to the crushing value formula: The crushing values ​​for each group were calculated, and the results are as follows: Figure 3 As shown. By Figure 3 It can be seen that, compared with uncarbonized steel slag, the crushing value of the carbonized steel slag prepared by this method is reduced, and its mechanical properties are improved.

[0136] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for rapidly producing high-quality steel slag aggregate, characterized by, The hierarchical carbonization process comprises the following steps: (1) Primary carbonization and reduction: using molten steel slag at 1300-1500℃ as raw material, continuously introducing industrial waste gas into the hot steaming tank during the water spraying cooling process for carbonization for 8-14h, while reducing the iron trioxide in the steel slag into iron and magnetite, to obtain primary carbonized steel slag; the industrial waste gas contains 20-30% CO2 and 30-60% CO by volume; (2) Secondary carbonization: selecting primary carbonized steel slag below 10mm as aggregate, placing it in a sealed container, spraying water on the steel slag aggregate according to a preset spraying amount, maintaining the pressure in the sealed container at 0.3-0.5MPa, and continuously introducing the same industrial waste gas into the sealed container for secondary carbonization, so that the free calcium oxide content in the steel slag aggregate is less than 3%; The high-quality steel slag aggregate after secondary carbonization is obtained by magnetic separation; the preset spraying amount in step (2) is 5-15% of the mass of the steel slag aggregate, and the secondary carbonization time is 1-12h; (3) Tertiary carbonization and / or quaternary carbonization, wherein the tertiary carbonization is spraying the secondary carbonized steel slag aggregate according to a preset spraying amount, maintaining the pressure in the sealed container at 0.3-0.5MPa, and continuously introducing the same industrial waste gas for carbonization for 3-6h to obtain tertiary carbonized steel slag aggregate; the quaternary carbonization is spraying the tertiary carbonized steel slag aggregate according to a preset spraying amount, maintaining the pressure in the sealed container at 0.3-0.5MPa, and continuously introducing the same industrial waste gas for carbonization for 1-2h; the tertiary carbonization and / or quaternary carbonization uses an acidic solution with a pH of 2-4 for spraying.

2. The method of quickly producing high-quality steel slag aggregate according to claim 1, wherein, The industrial waste gas is continuously introduced into the hot steaming tank in step (1) for carbonization for 10-12h to obtain primary carbonized steel slag.

3. The method of quickly producing high-quality steel slag aggregate according to claim 2, wherein, The industrial waste gas contains 20-25% CO2 and 35-50% CO by volume, and is continuously introduced into the hot steaming tank in step (1) for carbonization for 10h to obtain primary carbonized steel slag.

4. The method for quickly preparing high-quality steel slag aggregate according to claim 3, characterized in that, The preset spraying amount in step (2) is 10-15% of the mass of the steel slag aggregate, and the pressure in the sealed container in step (2) is maintained stable, and the same industrial waste gas is continuously introduced for carbonization for 6-9h.

5. The method of quickly producing high-quality steel slag aggregate according to claim 4, wherein, The preset spraying amount in step (3) is 10% of the mass of the steel slag aggregate, the pressure in the sealed container is maintained at 0.3MPa, the industrial waste gas is continuously introduced for carbonization for 3h during tertiary carbonization, and the industrial waste gas is continuously introduced for carbonization for 1h during quaternary carbonization.

6. A premium steel slag aggregate, characterized in that, The steel slag aggregate prepared according to the method of any one of claims 1-5 has a free calcium oxide content of less than 3.0% and an apparent relative density of 3.2-3.

3.

7. The premium steel slag aggregate of claim 6, wherein, The steel slag aggregate has a free calcium oxide content of 1.2-1.7% and an iron content of ≤1.1%.

8. Use of the steel slag aggregate of claim 6 or 7 in preparing asphalt concrete.

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