Method for accelerating carbonization of steel slag aggregate by using ultrasonic wave and alternating magnetic field

Abstract

The invention belongs to the technical field of road engineering, and particularly relates to a method for accelerating carbonization of a steel slag aggregate by using ultrasonic waves and an alternating magnetic field, which comprises the following steps: S1, pretreatment of the steel slag aggregate: adding water into steel slag in a sealed container, and fully aging; s2, carbonization reaction: transferring the pretreated steel slag aggregate into a carbonization stirring pot, injecting water until all the steel slag aggregate is immersed, and introducing sufficient CO2 gas into the carbonization stirring pot until the CO2 gas is uniformly distributed in the carbonization stirring pot; ultrasonic waves and an alternating magnetic field are applied to the steel slag, stirring is conducted for 60 min or above at the same time, and carbonization reaction is promoted; s3, taking out the carbonized steel slag from the carbonization stirring pot, and drying; through the synergistic effect of the ultrasonic waves and the alternating magnetic field, the carbonization efficiency of the steel slag aggregate is improved, precipitation and reaction of active components in the steel slag aggregate are promoted, growth and densification of carbonic acid crystals on the surface of the aggregate are further inhibited, and the stability and the utilization value of the steel slag aggregate are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of road engineering, and in particular relates to a method for accelerating the carbonization of steel slag aggregate by utilizing ultrasonic waves and alternating magnetic fields. Background Art

[0002] As an important industrial by-product, the comprehensive utilization of steel slag has always been a research focus in the field of resource recovery and environmental protection. Steel slag contains a large amount of free calcium oxide (f-CaO) and free magnesium oxide (f-MgO). These active components will undergo hydration reactions when exposed to water, resulting in volume expansion, which affects the stability and utilization value of steel slag. Traditional steel slag treatment methods, such as simple physical sorting and chemical stabilization treatment, can reduce its environmental impact to a certain extent, but they have not been able to fully solve the expansion problem caused by its internal active components.

[0003] At present, most carbonization studies focus on the transformation of steel slag powder, which has a large contact area and is easy to react with carbon dioxide (CO2) to form calcium carbonate (CaCO3) and magnesium carbonate (MgCO3), thereby reducing the expansion effect of its hydration reaction. However, these studies often ignore the direct application of steel slag aggregate. With the formal implementation of the national standard "General Portland Cement" GB175-2023, the application of steel slag powder in cement admixtures is restricted, and carbonized aggregate will be the main way to dispose of steel slag. Steel slag aggregate, especially aggregates with a size of 5.0 to 20.0 mm, has a wider range of engineering application prospects, such as use as aggregate in concrete and road construction. The precipitation and reaction efficiency of internal f-CaO and f-MgO of these aggregates directly determine their performance and stability in practical applications.

[0004] However, the carbonization reaction rate of steel slag aggregate is slow, and the precipitation of internal active components is insufficient, resulting in poor performance in practical applications. The traditional carbonization method has the following problems:

[0005] (1) The precipitation efficiency of active components inside steel slag aggregate is low, the cost of chemical activators is high, and there are environmental risks: Traditional methods are difficult to effectively promote the precipitation of f-CaO and f-MgO inside large-particle steel slag aggregates. Some aggregate carbonization methods require the addition of a large amount of chemical activators, such as ethylenediaminetetraethyl sodium, sodium citrate, acetic acid, etc., which have high treatment costs. In addition, the residual chemical activators will adhere to the surface of the aggregate. If not treated, it may pollute the environment.

[0006] (2) Slow carbonization reaction rate: The reaction rate of steel slag aggregate is slow in the traditional carbonization process. The wet method is often used to treat steel slag powder. However, the application of steel slag powder is limited.

[0007] (3) Crystal growth control problem: During the carbonization process, the size of CaCO3 and MgCO3 crystals is uncontrollable and they are easily attached to the surface of aggregates, resulting in densification of the aggregate surface and pore blockage, which inhibits the further precipitation and reaction of active components inside the aggregate and leads to a decrease in carbonization efficiency.

[0008] (4) Poor stability of steel slag aggregate: Since f-CaO and f-MgO expand when exposed to water, there are a large number of active ingredients inside the steel slag aggregate, which has poor stability.

[0009] Therefore, it is of great practical significance and application value to develop a new technology that can directly act on steel slag aggregate to accelerate the precipitation and carbonization reaction of f-CaO and f-MgO inside it. Summary of the invention

[0010] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for accelerating the carbonization of steel slag aggregate using ultrasound and an alternating magnetic field, thereby overcoming the particle size limitation of carbonization-treated steel slag and accelerating the carbonization reaction process.

[0011] In order to achieve the above object, the present invention provides the following technical solutions:

[0012] A method for accelerating the carbonization of steel slag aggregate using ultrasonic waves and alternating magnetic fields comprises the following steps:

[0013] S1. Pretreatment of steel slag aggregate: adding water to the steel slag in a sealed container for full aging;

[0014] S2. Carbonization reaction: Move the pretreated steel slag aggregate into a carbonization stirring pot, inject water until all the steel slag aggregate is submerged, and introduce sufficient CO2 gas into the carbonization stirring pot until the CO2 gas is evenly distributed in the carbonization stirring pot; apply ultrasonic waves and alternating magnetic fields to the steel slag, and stir for more than 60 minutes to promote the carbonization reaction;

[0015] S3. Take out the carbonized steel slag from the carbonization stirring pot and dry it.

[0016] Furthermore, in step S1, firstly, 10% to 11% water by mass is sprayed on the surface of the steel slag and stirred evenly, and then the steel slag aggregate is placed in a closed container at a humidity of more than 95% and a temperature of 25 to 30° C. for full aging for 24 hours.

[0017] Furthermore, in step S1, the particle size of the steel slag is controlled to be in the range of 0 to 30 mm.

[0018] Furthermore, in step S2, the pressure of CO2 gas introduced into the carbonization stirring pot is not less than 0.3Mpa, and the ultrasonic wave and alternating magnetic field are applied after ventilation for at least 30 minutes.

[0019] Furthermore, in step S2, the ultrasonic power applied to the steel slag is 100-150 W and the frequency is 20 kHz-50 kHz.

[0020] Furthermore, in step S2, the intensity of the alternating magnetic field applied to the steel slag is 0.04T to 0.06T.

[0021] Furthermore, for steel slag with a particle size of 0 to 5 mm, the ultrasonic power applied is 100 to 150 W, the frequency is 20 kHz to 50 kHz; the magnetic field strength applied is 0.02 to 0.06 T;

[0022] For steel slag with a particle size of 5 to 10 mm, the applied ultrasonic power is 100 to 150 W, the frequency is 20 kHz to 50 kHz, and the applied magnetic field strength is 0.02 to 0.06 T.

[0023] For steel slag with a particle size of 10 to 20 mm, the applied ultrasonic power is 100 to 150 W, the frequency is 20 kHz to 50 kHz, and the applied magnetic field strength is 0.02 to 0.06 T.

[0024] For steel slag with a particle size of 20 to 30 mm, the applied ultrasonic power is 100 to 150 W, the frequency is 20 kHz to 50 kHz; the applied magnetic field strength is 0.04 T.

[0025] Furthermore, the carbonization stirring pot includes a stirring pot body with an opening at the upper end, a stirring pot cover that can be installed at the opening and sealed, an alternating electromagnetic coil wrapped around the outer periphery of the stirring pot body, a plurality of ultrasonic transmitters arranged on the bottom surface of the stirring pot body, a CO2 ventilation pipe and a stirrer fixed on the stirring pot cover, and a gas pressure gauge and a control valve are installed on the CO2 ventilation pipe.

[0026] Furthermore, the carbonization stirring pot is made of cast iron.

[0027] Furthermore, the ultrasonic transmitters are arranged in the shape of a regular triangle on the bottom surface of the stirring pot.

[0028] The working principle of the present invention is to use ultrasound to accelerate the precipitation rate of f-CaO and f-MgO, and use an alternating magnetic field to control the crystal shape of CaCO3 to be mainly vaterite, with multiple attachment points and no aggregation, so that CaCO3 will not accumulate on the surface of steel slag particles, causing their surface densification.

[0029] The beneficial effects of the present invention are:

[0030] (1) Overcoming the limitation that carbonization treatment of steel slag can only be used for small particles below 5 mm: The present invention directly treats steel slag aggregate, breaking through the limitation of existing research that mainly treats steel slag powder. It can effectively improve the carbonization rate of large-size steel slag aggregate and reduce the free f-CaO and f-MgO inside the aggregate, providing a new way to utilize steel slag aggregate.

[0031] (2) Improving the stability of steel slag aggregate: Through the application of ultrasound, the present invention significantly improves the precipitation rate of f-CaO and f-MgO in steel slag aggregate, thereby accelerating the carbonization reaction process, inhibiting the expansion of steel slag aggregate when exposed to water, and improving the long-term stability of the aggregate.

[0032] (3) Limiting the crystal formation on the surface of steel slag aggregate: By utilizing the alternating magnetic field technology, the present invention effectively inhibits the excessive growth of CaCO3 crystals, avoids the precipitation and densification on the surface of the aggregate, maintains the open pore structure of the aggregate, helps the precipitation of free components inside the aggregate, and improves the carbonization degree of the aggregate.

[0033] (4) Reducing the disposal process and cost of steel slag aggregates: Since the method of the present invention improves the stability and application performance of aggregates, the need for pretreatment or stabilization of aggregates is reduced, thereby reducing the corresponding disposal costs.

[0034] (5) Resource and green utilization of steel slag: The steel slag aggregate, which was originally difficult to handle, is converted into building materials with practical application value, reducing the accumulation and management costs of waste. There is no need to add carbonizing surfactants, and only physical means such as alternating magnetic fields and ultrasound are used to promote the carbonization reaction, reducing the environmental problems that may arise during the disposal of steel slag aggregates. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0036] Figure 1 It is a structural schematic diagram of a carbonization stirring pot according to an embodiment of the present invention.

[0037] Figure 2 The figure is a schematic diagram of the top view of the upper cover of the stirring pot according to an embodiment of the present invention.

[0038] Figure 3 It is a schematic diagram of the bottom view of the stirring pot body according to an embodiment of the present invention.

[0039] Figure 4 is the Ca content in slag aggregate solution under different ultrasonic powers 2+ The precipitation concentration diagram;

[0040] Figure 5 This is a graph showing the pH value changes of steel slag aggregate leaching solution under different CO2 gas pressures.

[0041] Figure 6 This is a graph showing the relationship between conductivity and time under different electromagnetic induction intensities.

[0042] In the figure: 1- agitator motor; 2- sealing bolt; 3- sealing gasket; 4- water level line; 5- alternating electromagnetic coil; 6- insulating coating; 7- steel slag aggregate; 8- ultrasonic transmitter; 9- stirring pot body; 10- agitator blade; 11- stirring pot cover; 12- CO2 ventilation pipe; 13- sealing screw hole; 14- air pressure gauge and control valve. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0044] In the description of the present invention, the terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention. The terms "connected" and "connected" used in the present invention should be understood in a broad sense. For example, they can be fixed connections or detachable connections; they can be directly connected or indirectly connected through intermediate components. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0045] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0046] A method for accelerating the carbonization of steel slag aggregate using ultrasonic waves and alternating magnetic fields comprises the following steps:

[0047] S1. Pretreatment of steel slag aggregate: First, crush and screen the steel slag aggregate, and control the particle size of the steel slag aggregate within the range of 5.0 to 20.0 mm. Then, spray 10% to 11% (e.g., 10%, 10.5%, 11%) water by mass on the surface of the steel slag, stir evenly, and then place the steel slag aggregate in a closed container at a humidity of more than 95% and a temperature of 25°C to 30°C for full aging for 24 hours.

[0048] S2. Carbonization reaction: Move the pretreated steel slag aggregate into the carbonization mixing pot and inject enough water until all the steel slag aggregate is submerged; note that the aggregate volume should not exceed 1 / 2 of the container, and the liquid level should not exceed 2 / 3 of the mixing tank volume. Figure 1 The water level line is shown in the figure; then, carbon dioxide (CO2) gas with a pressure of more than 0.3MPa is introduced into the carbonization stirring pot for more than 30 minutes to ensure that the gas is evenly distributed in the container; then, the ultrasonic transmitter is started to apply ultrasonic waves with a power of 100-150W and a frequency of 20kHz-50kHz, and an alternating magnetic field with a frequency of 50Hz and an intensity of 0.04T-0.06T to the steel slag aggregate, and the stirring rate is 30rpm for 60 minutes; the ultrasound accelerates the precipitation of f-CaO and f-MgO and promotes the carbonization reaction; the alternating magnetic field inhibits the growth of CaCO3 crystals on the surface of the steel slag aggregate, and generates large-sized and low-density vaterite crystals, which will not adhere to the surface of the aggregate to cause its densification;

[0049] S3. The carbonized steel slag is taken out from the carbonization stirring pot and dried. Since the present invention promotes the carbonization reaction by purely physical means without adding chemical additives, the steel slag only needs to be air-dried (of course, other drying methods such as drying, spinning, etc. can also be used, but with higher energy consumption).

[0050] Specifically, due to the different particle sizes of steel slag, for steel slag with a particle size of 0 to 5 mm, the applied magnetic field strength is 0.02 to 0.06 T; for steel slag with a particle size of 5 to 10 mm, the applied magnetic field strength is 0.02 to 0.06 T; for steel slag with a particle size of 10 to 20 mm, the applied magnetic field strength is 0.02 to 0.06 T; for steel slag with a particle size of 20 to 30 mm, the applied magnetic field strength is 0.04 T.

[0051] like Figures 1 to 3 As shown, the carbonization stirring pot includes a stirring pot body with an opening at the upper end, a stirring pot cover that can be installed at the opening and sealed, an alternating electromagnetic coil wrapped around the outer periphery of the stirring pot body, a plurality of ultrasonic transmitters arranged in the bottom surface of the stirring pot body, a CO2 ventilation pipe and a stirrer fixed on the stirring pot cover, the CO2 ventilation pipe is equipped with a gas pressure gauge and a control valve; the stirrer includes a stirrer motor installed at the center of the stirring pot cover, a stirrer shaft rotatably installed at the center of the stirring pot cover, and stirrer blades fixed on the stirrer shaft, and the stirrer motor drives the stirrer blades to rotate.

[0052] The carbonized stirring pot is made of cast iron, which can concentrate magnetic field lines and improve electromagnetic performance; the outer periphery of the stirring pot body is coated with an insulating coating to prevent the stirring pot body from conducting electricity and ensure the safety of operators; the alternating electromagnetic coil is made of copper core enameled wire spirally wound outside the stirring pot body. The upper edge of the stirring pot body and the edge of the stirring pot cover are both provided with edge rings, threaded mounting holes are provided on the edge ring of the stirring pot body, and circular mounting holes are provided on the edge ring of the stirring pot cover. A sealing ring is also embedded in the inner ring of the stirring pot cover, so that the stirring pot body and the stirring pot cover can be connected by sealing bolts to achieve the sealing of the carbonized stirring pot.

[0053] The ultrasonic transmitters are arranged in an equilateral triangle on the bottom of the stirring pot; in the laboratory scenario of this experiment, a stirring pot with a diameter of about 30 cm can be used, and the distance between the ultrasonic transmitters is 20 cm; for medium and large equipment, the distance between each ultrasonic transmitter can be increased to 20-30 cm, the number of transmitters is adjusted according to the diameter of the pot, and the power of a single ultrasonic generator can also be increased from 100W. For factories or engineering production, the ultrasonic generator can also be installed on the inner wall of the side wall, and a magnetic field can be applied to the bottom or a magnetized circulating water process can be used.

[0054] It should be noted that the raw material used in the present invention is steel slag recovered from a steel plant, and the steel slag has been magnetically separated. For highway asphalt mixtures, the aggregate particle size is generally within 20 mm, so the crushing and screening of the steel slag is within this range. The alternating electromagnetic field in the present invention can be directly powered by commercial electricity (220V, 50Hz), and no additional frequency conversion equipment is required, thereby avoiding increased energy consumption and equipment costs during the conversion process. Considering that the carbonization stirring pot is usually made of pig iron, the alternating magnetic field will cause the stirring pot to heat up. After testing, the use of an alternating magnetic field of 0.04T will not cause the temperature of the carbonization stirring pot to rise sharply due to the heat dissipation of the environment and the carbonization stirring pot itself. After 60 minutes of continuous reaction at room temperature, the temperature only rises by 5 to 10°C, so this temperature change has little effect on the entire treatment result, and considering energy saving and environmental protection, the present invention does not make further research on the temperature factor.

[0055] The present invention aims to improve the carbonization efficiency of steel slag aggregates through the synergistic effect of ultrasonic waves and alternating magnetic fields, promote the precipitation and reaction of active components inside the aggregates, and further inhibit the growth and densification of carbonate crystals on the aggregate surface, reduce the content of internal f-CaO and f-MgO, thereby significantly improving the stability and utilization value of steel slag aggregates. Through this innovative method, the present invention can not only improve the environmental adaptability and engineering application performance of steel slag aggregates, but also promote the high-value utilization of by-products of the steel industry, making positive contributions to environmental protection and resource conservation.

[0056] Preliminary experiment 1

[0057] In order to explore the Ca content of the solution under different ultrasonic powers 2+ The influence of precipitation concentration on the precipitation of carbonization was investigated by adding steel slag aggregate with a particle size of 5 to 20 mm into a carbonization stirring pot. The Ca content of the solution was measured after ultrasonic stirring for 60 minutes without the introduction of CO2 gas. 2 + The precipitation concentration from Figure 4 As can be seen from the figure, with the ultrasound turned on, the Ca in the leaching solution of steel slag aggregate 2 + precipitation concentration increased significantly, and when the ultrasonic power reached 100W, Ca 2+ The precipitation concentration reaches a stable level. Therefore, in order to optimize the economic benefit and disposal efficiency, the optimal ultrasonic power should be 100W.

[0058] Preliminary Experiment 2

[0059] In order to explore the change of pH value of 5-20mm steel slag aggregate leaching solution over time under different CO2 gas pressures. By introducing CO2 gas at different pressures, the time required for the steel slag leaching solution to reach the maximum pH value will be shortened, and the pH peak value will also be reduced. During the laboratory experiment, under the conditions of 100W and 20kHz ultrasound, 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, and 0.5MPa were introduced into the sealed carbonization stirring pot respectively. The results are as follows Figure 5 shown.

[0060] The pH value in the result reflects the Ca content in the slag leaching solution. 2+Crystallization degree. Since f-CaO and f-MgO in steel slag are alkaline substances, the pH value of the steel slag leachate will first increase and then decrease over time. The main reason for this change is that f-CaO and f-MgO in steel slag first precipitate to form Ca(OH)2 and Mg(OH)2 under the action of ultrasound, resulting in a rapid increase in pH value; then these alkaline substances react with CO2 to form CaCO3 and MgCO3, thereby reducing the pH value of the precipitate. At the same time, as the CO2 pressure increases to 0.3MPa, the time required for the steel slag leachate to reach the maximum pH value gradually shortens, and the pH peak value also decreases significantly, and the pH change rate after the peak is significantly higher than that of the case less than 0.3MPa. This shows that when the CO2 pressure is 0.3MPa, the alkaline substances in the steel slag leachate can fully react with the CO2 gas to reach a crystallization equilibrium, and then with the introduction of CO2 gas, the precipitation rate of active alkaline substances is less than the dissolution rate of CO2, so the pH value of the solution is significantly reduced. In addition, according to the curve of pH value changing with time when CO2 pressure is not less than 0.3MPa, it can be seen that when the test time reaches 60 minutes, the pH value of the leaching solution is lower than the pH value of the initial leaching solution, and the change amplitude of the subsequent curve is small. It can be considered that the carbonization reaction has basically ended, and 60 minutes can be considered as the time required for the pH value of the precipitated solution to reach stability.

[0061] In this preliminary experiment 2, by comparison, it was obtained that the Ca content in steel slag 2+ The CO2 pressure value that first reaches crystallization equilibrium accelerates the carbonization process. For different steel slags, the pH peak values ​​of their leaching solutions are also different, but the optimal CO2 pressure can still be determined to be 0.3MPa by the time to reach the peak value.

[0062] Preliminary Experiment 3

[0063] In order to explore the relationship between the final conductivity under different alternating magnetic field strengths, for steel slag aggregate with a particle size of 5 to 20 mm, under the conditions of 0.3 MPa CO2, 20 KHz, 100 W ultrasonic wave, the magnetic field strengths of 0 T, 0.01 T, 0.02 T, 0.03 T, 0.04 T, 0.05 T, and 0.06 T were compared, and the treatment time was 60 minutes. The results are as follows Figure 6 As shown, compared with the untreated solution (under 0T conditions), the conductivity of the solution after alternating magnetic field treatment is lower, indicating that the crystallization effect of CaCO3 and MgCO3 is good, among which the best crystallization effect can be achieved under 0.03T~0.05T conditions.

[0064] Verification example:

[0065] According to the method of GB / T 38216.3-2023, EDTA titration is used to determine the free calcium oxide content of steel slag before and after treatment. The difference between the free calcium oxide content before and after treatment and the free calcium oxide content before treatment are the carbonization degree of steel slag aggregate.

[0066] In this verification example, in order to obtain the treatment effect of the present invention on steel slag aggregate, steel slag of 5 to 20 mm was screened for verification. The treatment conditions were: 100W, 20kHz ultrasound, 50Hz, 0.04T alternating magnetic field, 0.3MPa CO2, treatment time 60min. The results are shown in Table 1.

[0067] Table 1 Carbonization degree of steel slag aggregate after treatment

[0068] f-CaO content before treatment (%) f-CaO content after treatment (%) Carbonization degree (%) 6.85 1.74 74.60

[0069] The carbonization degree of steel slag aggregate treated with CO2 is generally about 20%. The carbonization degree of steel slag aggregate treated with the method of the present invention is 74.6%, which significantly improves the carbonization rate of steel slag aggregate. Generally, the free calcium oxide content of steel slag aggregate is required to be less than 3%, that is, the carbonization degree of aggregate is required to be greater than 56.2%, that is, to meet the engineering requirements. Therefore, the steel slag aggregate treated with the method of the present invention can be used as aggregate in concrete and road construction.

[0070] Comparative test

[0071] In order to explore the influence of different influencing factors, such as particle size range (mm), ultrasonic power (W), alternating magnetic field intensity (T), and CO2 pressure (MPa), on the carbonization degree of steel slag aggregate, the L16 (4*4) orthogonal test table was used to carry out orthogonal test analysis of the carbonization treatment results of 0-30 mm steel slag. When the stirring rate was kept at 30 rpm and the carbonization time was 60 minutes, the test design and results were shown in Table 2. In Table 2, the tests whose carbonization degree after treatment met the engineering requirements were recorded as qualified, and those that did not were recorded as unqualified. In each test, the steel slag of the corresponding particle size was first screened and then treated under the corresponding conditions.

[0072] Table 2 Orthogonal experimental design and results

[0073]

[0074] From the table above we can see that:

[0075] (1) Effect of particle size range: The results show that the carbonization degree decreases significantly with the increase of particle size range. For example, the carbonization degree of the test with a particle size range of 0-5 mm is generally higher than the results of other particle size ranges under similar treatment conditions. In particular, the carbonization degree of test 3 (0-5 mm particle size, 100W ultrasonic wave, 0.04T alternating magnetic field, 0.4MPa CO2) is as high as 86.54%, which is the highest among all the tests.

[0076] (2) Influence of ultrasonic power: The increase of ultrasonic power helps to improve the carbonization degree, but it is affected by the particle size effect and there is a phenomenon of diminishing marginal utility. For example, the carbonization degree of test 3 (0-5mm particle size, 150W ultrasonic) is 80.15%, and the carbonization degree of test 7 (5-10mm particle size, 100W ultrasonic) is 69.14%. According to the previous pre-experiments 1 and 2 of different ultrasonic intensities and CO2 pressures, the treatment effects under 100W and 150W ultrasonic conditions are similar, and the carbonization treatment effects under 0.3MPa and 0.4MPa CO2 pressures are similar, but the 0-5mm test 3 has a higher carbonization degree than the 5-10mm test 7. In tests 11 and 15, the treated particle size ranges are 10-20mm and 20-30mm, respectively. The treatment effects of ultrasonic power are similar, and the alternating magnetic field and CO2 pressure are the same. The test results of test 11 are qualified, and those of test 15 are unqualified. This indicates that with the increase of slag particle size, the effect of increasing ultrasonic power on improving the carbonization degree is weakened.

[0077] (3) Effect of alternating magnetic field intensity: When the alternating magnetic field intensity is 0.04 T, the carbonization degree is higher. This is consistent with the results of the previous alternating magnetic field preliminary test 3. For example, compared with similar treatment conditions, higher carbonization results can be obtained under test 3 and test 16, and the highest carbonization results can be obtained for 0-5 mm and 20-30 mm steel slag aggregates.

[0078] (4) Effect of CO2 pressure: When the CO2 pressure is less than 0.3 MPa, the carbonization degree gradually increases. The CO2 pressures of Tests 12 and 15 were both below 0.3 MPa, and the carbonization degrees were 62.47% and 49.31%, respectively, which were significantly lower than the results of Test 7 (carbonization degree 69.14%) and Test 16 (carbonization degree 64.45%) under similar treatment conditions. When the CO2 pressure was greater than 0.3 MPa, the carbonization degree did not change much, such as Tests 3 and 4, Tests 8 and 11, and Tests 5 and 13.

[0079] (5) Combined effect of ultrasound and alternating magnetic field: Under the combined effect of ultrasound and alternating magnetic field, the carbonization degree is significantly higher than that when only ultrasound or alternating magnetic field is used. The carbonization degree of tests 2, 3 and 4, 6, 7, 10, 12, 15 and 16 is relatively high, with the lowest carbonization degree not less than 42.67% (test 10), while the maximum carbonization degree of the tests using CO2 and single ultrasound or alternating magnetic field conditions (tests 5, 8, 9, 11, 13, 14) does not exceed 18.45% (test 8), which is consistent with the expected law.

[0080] In general, the particle size range has the most significant effect on the carbonization degree, followed by the alternating magnetic field intensity and ultrasonic power. The effect of CO2 pressure in different tests is relatively small, but it may interact with other factors to affect the carbonization effect.

[0081] According to the specification requirements, the content of f-CaO should be less than 3%, that is, the carbonization degree of the aggregate is required to be greater than 56.2%. From Table 2, it can be seen that the carbonization degrees of the tests 3, 4, 7, 12, and 16 are qualified, and the rest are unqualified test conditions. The results show that: (1) If ultrasonic waves and / or alternating magnetic fields are not used, the carbonization degree of the steel slag aggregate should be less than 20%; (2) In the table, the carbonization degree of the steel slag aggregate with an ultrasonic power lower than 100W does not meet the requirements of the specification, while when the ultrasonic power is greater than 100W and the alternating magnetic field intensity is 0.04T, the carbonization degree of the steel slag aggregate with a size of 0 to 30mm can meet the requirements of the specification. Therefore, the results in Table 2 also prove the advantages of the method proposed by the present invention, and the preferred parameters adopted can meet the requirements of steel slag aggregate carbonization.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for accelerating the carbonization of steel slag aggregate using ultrasonic waves and alternating magnetic fields, characterized in that: The following steps are involved: S1. Pretreatment of steel slag aggregate: adding water to the steel slag in a sealed container for full aging; S2. Carbonization reaction: Move the pretreated steel slag aggregate into a carbonization stirring pot, inject water until all the steel slag aggregate is submerged, and introduce sufficient CO2 gas into the carbonization stirring pot until the CO2 gas is evenly distributed in the carbonization stirring pot; apply ultrasonic waves and alternating magnetic fields to the steel slag, and stir for more than 60 minutes to promote the carbonization reaction; S3. Take out the carbonized steel slag from the carbonization stirring pot and dry it.

2. The method for accelerating carbonization of steel slag aggregate by using ultrasonic waves and alternating magnetic fields according to claim 1, characterized in that: In step S1, firstly, 10% to 11% water by mass is sprayed on the surface of the steel slag and stirred evenly, and then the steel slag aggregate is placed in a closed container at a humidity of more than 95% and a temperature of 25 to 30° C. for full aging for 24 hours.

3. The method for accelerating carbonization of steel slag aggregate by using ultrasonic waves and alternating magnetic fields according to claim 1, characterized in that: In step S1, the particle size of the steel slag is controlled within the range of 0 to 30 mm.

4. The method for accelerating carbonization of steel slag aggregate by using ultrasonic waves and alternating magnetic fields according to claim 1, characterized in that: In step S2, the pressure of CO2 gas introduced into the carbonization stirring pot is not less than 0.3Mpa, and the ultrasonic wave and alternating magnetic field are applied after ventilation for at least 30 minutes.

5. The method for accelerating carbonization of steel slag aggregate by using ultrasonic waves and alternating magnetic fields according to claim 1, characterized in that: In step S2, the ultrasonic wave power applied to the steel slag is 100-150W and the frequency is 20kHz-50kHz.

6. The method for accelerating carbonization of steel slag aggregate by using ultrasonic waves and alternating magnetic fields according to claim 1, characterized in that: In step S2, the intensity of the alternating magnetic field applied to the steel slag is 0.04T to 0.06T.

7. The method for accelerating carbonization of steel slag aggregate by using ultrasonic waves and alternating magnetic fields according to claim 1, characterized in that: For steel slag with a particle size of 0 to 5 mm, the applied ultrasonic power is 100 to 150 W, the frequency is 20 kHz to 50 kHz, and the applied magnetic field strength is 0.02 to 0.06 T; For steel slag with a particle size of 5 to 10 mm, the applied ultrasonic power is 100 to 150 W, the frequency is 20 kHz to 50 kHz, and the applied magnetic field strength is 0.02 to 0.06 T. For steel slag with a particle size of 10 to 20 mm, the applied ultrasonic power is 100 to 150 W, the frequency is 20 kHz to 50 kHz, and the applied magnetic field strength is 0.02 to 0.06 T. For steel slag with a particle size of 20 to 30 mm, the applied ultrasonic power is 100 to 150 W, the frequency is 20 kHz to 50 kHz; the applied magnetic field strength is 0.04 T.

8. The method for accelerating carbonization of steel slag aggregate by using ultrasonic waves and alternating magnetic fields according to claim 1, characterized in that: The carbonization stirring pot comprises a stirring pot body with an opening at the upper end, a stirring pot cover which can be installed at the opening and sealed, an alternating electromagnetic coil wound around the stirring pot body, a plurality of ultrasonic transmitters arranged in the bottom surface of the stirring pot body, a CO2 ventilation pipe fixed on the stirring pot cover and a stirrer, wherein the CO2 ventilation pipe is equipped with a gas pressure gauge and a control valve.

9. The method for accelerating carbonization of steel slag aggregate by using ultrasonic waves and alternating magnetic fields according to claim 8, characterized in that: The carbonization stirring pot is made of cast iron.

10. The method for accelerating carbonization of steel slag aggregate by using ultrasonic waves and alternating magnetic fields according to claim 8, characterized in that: The ultrasonic transmitters are arranged in a regular triangle on the bottom surface of the stirring pot.

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