A method for full-process modification of molten steel slag with carbon dioxide under normal pressure

Abstract

This invention relates to a method for modifying molten steel slag with carbon dioxide throughout the entire process under normal pressure. The method includes: first, adding the first batch of steel slag to a slag pot for melting; then, adding 10%–35% of the mass of the first batch of hot molten steel slag as a steel slag fracturing agent to the slag pot; next, unloading a second batch of hot molten steel slag into the slag pot through a slag discharge device of a converter or continuous casting system; then, adding a second batch of hot molten steel slag as a steel slag fracturing agent to the slag pot, repeating this cycle until the slag pot is full. This method achieves complete dissociation and efficient separation of the molten steel slag by adding modified steel slag tailings and steel slag fracturing agent in layers into the slag pot, utilizing the phased and temperature-segmented release of carbon dioxide by the fracturing agent. This completely solves the problems of iron-rich casting residue, desulfurization slag welding pot, and agglomeration. This method can be combined with the phased supply of solid carbon dioxide to synergistically improve the strength of the steel slag. The residue after supply can be utilized as a resource, making it environmentally friendly and efficient.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical environmental protection and relates to a method for modifying molten steel slag with carbon dioxide throughout the entire process under normal pressure. In particular, it relates to a method and equipment system for continuously releasing carbon dioxide in stages and temperature ranges under normal pressure to modify molten steel slag throughout the entire process. Background Technology

[0002] Since the 1950s, my country has experimented with various stabilization processes for hot steel slag, including hot pouring, hot quenching, air quenching, water quenching, wheel quenching, and drum quenching, culminating in the currently popular pressurized hot quenching process. These processes have significantly improved the stability of steel slag during its transformation from a molten to a solid state, and have even led to the development of a series of patented technologies targeting specific properties of steel slag, thus driving technological advancements in steel slag treatment.

[0003] Patent application CN111853235A discloses a locking device and method for a large-diameter vertical pressurized hot slag jar. The locking device includes a jar lid, lid flange, jar body flange, lid positioning seat, slide rail, jar body slider, and rotary cylinder support. The locking device uses the extension and retraction of the rotary cylinder to move the jar body slider within the slide rail. The lid positioning seat and the jar body slider follow these movements to achieve both lid locking and unlocking functions, forming part of the quick-opening function of the large-diameter hot slag jar. The patent applicant also disclosed a series of processes and devices for pressurized hot slag processing, contributing to the maturity of pressurized hot slag technology. However, in practice, it has been found that when using pressurized hot slag processing technology, water vapor in the reactor reacts with metallic iron in the slag over a long period, generating non-magnetically separable iron oxide or iron hydroxide, preventing efficient recovery of iron resources from the slag. Therefore, the key to hot-melt steel slag treatment is how to prevent the metallic iron phase in the molten state from transforming into the ferric oxide phase.

[0004] To address the challenge of phase transformation in the treatment of molten hot steel slag, many experts and scholars in my country have conducted numerous trials and invented many new technologies and methods. For example, invention patent application CN 119241101 A discloses a quenching and modifying agent for molten vanadium-containing steel slag. This quenching and modifying agent comprises: component A: Si powder; component B: mainly CaF2; and component C: mainly quicklime, Na2O, and K2O. This quenching and modifying agent is mainly used directly on molten vanadium-containing steel slag during converter slag discharge, fully utilizing the residual heat of the molten steel slag. By adding the quenching and modifying agent, the final product of the vanadium-containing steel slag meets the application standards for cement clinker. This patent maintains the silicate characteristics of steel slag, especially vanadium-containing steel slag, under normal pressure. Its shortcoming is that it does not include a design for the separation of iron and slag in the steel slag.

[0005] The invention patent with publication number CN 118515443 A discloses a method for improving the magnetic separation rate and cementitious activity of steel slag. During converter slag discharge, molten steel slag and a mineral phase regulator are simultaneously poured into a slag pot, resulting in a CaO / SiO2 mass ratio of 2–3 in the steel slag. The cooling regime is controlled, with a cooling rate of 1–6 °C / min from 1550–1650 °C to 1300 °C. After holding at 1300 °C for 1–6 hours, the slag is cooled to room temperature at a rate greater than or equal to 800 °C / min to increase the proportion of magnetic and cementitious phases in the steel slag. After online conditioning and modification, the steel slag is magnetically separated to recover iron resources, achieving a magnetic separation rate of 40%–50%. The magnetic separation tailings can be used as a high-quality admixture in the preparation of various building materials. This method can synergistically achieve efficient recovery of iron resources from steel slag and enhance cementitious activity, improving the resource utilization level of steel slag and overcoming the limitations of its use in cement and other building materials. However, this patent uses air cooling to modify steel slag, which takes a relatively long time.

[0006] Patent application CN 118326110 A discloses a method for modifying steel slag in a converter furnace. Based on the varying basicity of the steel slag within the converter, different amounts of silica powder are added to alter the slag's basicity. Subsequently, air is injected to provide an oxidizing atmosphere to eliminate f-CaO in the slag. Furthermore, the oxidizing atmosphere facilitates the transformation of the iron-bearing ore phase from non-magnetic FeO to magnetic Fe3O4 and Fe2O3, thereby improving the magnetic separation recovery rate of iron in the steel slag. This invention effectively eliminates f-CaO in steel slag, improves its cementing properties, and aids in iron recovery. Moreover, this invention offers high efficiency, ease of operation, and low investment costs. A drawback of this invention is that utilizing converter furnace conditions for steel slag modification may negatively impact slag discharge and production efficiency in steelmaking.

[0007] In summary, existing steel slag modification technologies mainly focus on removing free calcium oxide during the transformation of steel slag from a molten state to a solid state, ensuring its usability in the building materials industry. However, significant shortcomings remain in practical applications: First, traditional water treatment and steam treatment processes easily cause oxidation of metallic iron, making efficient recovery difficult and posing safety hazards; second, existing modifiers generally suffer from problems such as a single gas production temperature, short duration, and insufficient carbon dioxide supply, failing to match the entire cooling process of steel slag from high to low temperatures. This results in highly adhesive steel slags such as iron-rich casting residue and desulfurization slag still exhibiting phenomena such as weld pooling, clumping, and difficulty in crushing; third, most processes do not adequately consider both steel slag treatment efficiency and the carbon reduction and environmental protection needs of steel enterprises. To address this, the present invention proposes a method and equipment system for modifying molten steel slag under a carbon dioxide atmosphere at atmospheric pressure. By continuously releasing carbon dioxide in stages and temperature ranges through a steel slag shaving agent, the molten steel slag is kept non-adhesive throughout the process, and steel is efficiently separated. This fundamentally solves the problems of welding pots and clumping, while improving the recovery rate of metallic iron, reducing processing energy consumption and emissions, and meeting the development needs of steel enterprises for green, low-carbon, and efficient utilization of steel slag. Summary of the Invention

[0008] In view of this, in order to solve the problems of existing steel slag treatment technologies, such as oxidation of metallic iron due to water / steam environment, low recovery rate and explosion hazard, or mismatch of modifier production temperature zone and inability to cover the entire cooling process, resulting in easy clumping of weld pots, and difficulty in balancing treatment efficiency, iron recovery and carbon reduction and environmental protection requirements, this invention provides a method for full-process modification of molten steel slag with carbon dioxide under normal pressure. This method will maximize the preservation of metallic iron in steel slag from oxidation, thereby enabling its recycling and achieving safety and ecological benefits in steel slag treatment operations in steel enterprises.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for modifying molten steel slag with carbon dioxide at atmospheric pressure throughout the entire process includes: first, adding the first batch of steel slag to a slag pot for melting; then, adding 10%–35% (by weight of the first batch of hot molten steel slag) of a steel slag shaving agent to the slag pot; after the first batch is added, allowing it to stand for at least 60 minutes; then, unloading the second batch of hot molten steel slag into the slag pot through a slag discharge device of a converter or continuous casting system; then, adding 10%–35% (by weight of the second batch of hot molten steel slag) of a steel slag shaving agent to the slag pot; and finally, allowing it to stand for at least 60 minutes after the second batch is added. The process is repeated until the slag pot is full. The steel slag shaving agent is a combination of substances that generate carbon dioxide atmosphere in stages. Its main components include quicklime that releases carbon dioxide in the range of 1350-1580℃, industrial-grade sodium bicarbonate that releases carbon dioxide in the range of 900-1100℃, and secondary aluminum ash that releases carbon dioxide below 800℃. Through the combination of quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash, a stepped gas release mode is achieved, which includes simultaneous gas production of three components at high temperature, continuous gas production of two components at medium temperature, and stable gas production of one component at low temperature. This provides continuous, stable, and stratified carbon dioxide atmosphere protection throughout the cooling process of steel slag, maximizing the preservation of metallic iron in the steel slag from oxidation, thus enabling its recycling. Furthermore, there are no harmful residues after the quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash supply carbon dioxide. The reaction products can also improve the strength of steel slag and achieve full resource utilization.

[0011] Furthermore, the temperature of the hot-state molten steel slag is in the range of 1350–1580℃. Quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash decompose simultaneously, releasing carbon dioxide. Quicklime decomposition is dominant, forming a dense gas film on the surface of the molten slag, preventing the molten slag from sticking together. 30–60 minutes after the hot-state molten steel slag is fed, the temperature inside the slag pot drops to 900–1100℃. The quicklime is basically decomposed, while the industrial-grade sodium bicarbonate and secondary aluminum ash continue to decompose and release carbon dioxide, breaking down the internal binding force of the steel slag and achieving loosening and dissociation of the slag body. 60 minutes after the hot-state molten steel slag is fed, the temperature inside the slag pot is below 800℃. Only the secondary aluminum ash continuously and stably releases a large amount of carbon dioxide, keeping the steel slag in a loose and non-sticky state in the slag pot for a long time. At the same time, the carbon dioxide gas flow continuously impacts and disturbs the slag body, causing steel, iron, and other metals to be fully separated and dispersed from the slag, forming independent steel particles, achieving efficient separation of steel and slag.

[0012] Furthermore, the time interval between the two hot-melt steel slag throws is 30 to 60 minutes, with the optimal interval being 60 minutes.

[0013] Furthermore, the main components of the steel slag crushing agent, by mass percentage, include: 40%~60% quicklime, 10%~30% industrial-grade sodium bicarbonate, and 10%~30% secondary aluminum ash. The above components are made into spherical particles of 5~15mm by sintering and pelletizing process.

[0014] Furthermore, the main components of the steel slag shaving agent, by mass percentage, include: 40%~60% quicklime, 10%~20% industrial-grade sodium bicarbonate, 10%~25% secondary aluminum ash, and 5%~10% 80~150 mesh CaF2 powder. The above components are made into spherical particles of 5~15mm using a sintering and pelletizing process. Among them, CaF2 powder can reduce the molten viscosity of steel slag, promote the rapid dispersion and penetration of the shaving agent, and improve the uniformity of carbon dioxide release. Appropriately increasing the CaF2 content can further enhance the high-temperature fluxing and low-temperature pore-forming effects, making the steel slag easier to loosen and dissociate, and the steel-slag separation more complete.

[0015] Furthermore, secondary aluminum ash is a waste product generated after the remelting of primary aluminum ash or the recycling of aluminum ingots. It has a low content of metallic aluminum, and its chemical composition by mass percentage is as follows: Al2O3: 62.5~65.2%, Na2O: 8.2~9.0%, CaO: 3.4~3.8%, SiO2: 2.4~2.8%, MgO: 5.4~5.9%, TiO2: 1.70~1.95%, SO3: 1.6~1.8%, K2O: 1.1~1.3%, Fe2O3: 0.5~0.58%.

[0016] Furthermore, the steel slag crushing agent is thrown using a crushing agent feeding device system. This system includes a conveyor belt whose output end is connected to the steel slag slag tank, a support for supporting the conveyor belt, a base for supporting the support, and a metering scale set on one side of the input end of the conveyor belt. A monitoring device for monitoring the throwing of steel slag crushing agent on the conveyor belt is set on the support on the output end of the conveyor belt.

[0017] Furthermore, the modified steel slag has a honeycomb porous structure, is easy to break and grind, and can be directly used as a high-calcium cement admixture, concrete admixture, and sludge solidification agent.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. The method for modifying molten steel slag with carbon dioxide under normal pressure disclosed in this invention employs a staged gas production design using a compound of quicklime, industrial-grade sodium bicarbonate, and secondary alumina ash as the steel slag crushing agent. This design precisely matches the natural cooling curve of the steel slag from 1350~1580℃ to 900~1100℃ to <800℃: In the high-temperature stage, quicklime, sodium bicarbonate, and secondary alumina ash simultaneously produce gas, with quicklime forming a gas film to prevent slag from sticking together; in the medium-temperature stage, sodium bicarbonate and secondary alumina ash continuously produce gas, breaking down the internal binding force of the slag; in the low-temperature stage, only secondary alumina ash stably produces gas to maintain the looseness of the slag, while airflow disturbance promotes the separation of metallic iron from the slag phase. This three-layer effect runs through the entire steel slag cooling process, completely solving the industry pain points of traditionally difficult-to-treat steel slags such as rich iron casting residue slag and desulfurization slag, which are prone to welding, clumping, and difficult to crush.

[0020] 2. The method for modifying molten steel slag under atmospheric pressure using carbon dioxide throughout the entire process disclosed in this invention replaces the traditional water / steam treatment process with a dry CO2 atmosphere. This avoids the reaction of iron with water at high temperatures to form non-magnetically separable iron oxide and iron hydroxide. Furthermore, the continuous impact and dispersion effect of the CO2 gas flow prevents the rapid settling and enrichment of molten iron into large iron lumps, ensuring that metallic iron is uniformly dispersed in the slag as independent steel particles. After implementation, the iron content of the steel slag tailings can be reduced to below 1.2%, and the recovered iron particle grade reaches 89.6%~92.5%. Only simple magnetic separation is required to achieve efficient steel slag separation, significantly improving the iron resource recovery rate compared to the traditional pressurized hot quenching process. Moreover, the quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash leave no harmful residues after being supplied with carbon dioxide, and the reaction products can also improve the strength of the steel slag, achieving full resource utilization.

[0021] 3. The method for modifying molten steel slag with carbon dioxide under normal pressure disclosed in this invention eliminates the need for subsequent water-cooling and quenching processes, thus fundamentally eliminating the safety hazard of water vapor explosion. It also produces no wastewater or dust emissions, simultaneously meeting the carbon reduction and emission reduction needs of steel enterprises. Furthermore, the modified steel slag exhibits a honeycomb porous structure, significantly improving its grindability and activity. It can be directly used as a high-calcium cement admixture, concrete admixture, and sludge solidification agent without complex processing, shortening the steel slag treatment process, reducing energy consumption, and greatly improving the utilization rate of high-value-added steel slag resources.

[0022] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0024] Figure 1 This is a schematic diagram of the structure of the slag-crushing agent feeding device system of the present invention;

[0025] Figure 2 This is a natural cooling curve of molten steel slag in this invention. The curve shows the temperature change pattern of molten steel slag in this invention from a high temperature range of 1350℃ to 1580℃, through a medium temperature range of 900℃ to 1100℃, and then to a low temperature range below 800℃. This temperature range is completely matched with the temperature range of the three-stage temperature zone gas generation and step-by-step dissociation of steel slag by the steel slag crushing agent.

[0026] Attached reference numerals: 1. Support frame; 2. Measuring scale; 3. Conveyor belt; 4. Monitoring and control device; 5. Base; 6. Steel slag hopper. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] Example 1

[0029] This invention provides a method for modifying molten steel slag under atmospheric pressure and carbon dioxide atmosphere throughout the entire process, comprising: throwing 100 kg of the first batch of modified steel slag tailings into a steel slag slag jar; then throwing 10% of the mass of the first batch of hot molten steel slag with steel slag shaving agent into the steel slag jar; unloading the second batch of hot molten steel slag into the steel slag jar through the slag unloading device of a converter or continuous casting system; then throwing the second batch of hot molten steel slag with 10% of the mass of steel slag shaving agent into the steel slag jar; and repeating this cycle until the slag jar is full. The steel slag shaving agent is a combination of substances that generate a carbon dioxide atmosphere in stages. Its main components include quicklime, which releases carbon dioxide in the range of 1350-1580℃; industrial-grade sodium bicarbonate, which releases carbon dioxide in the range of 900-1100℃; and secondary aluminum ash, which releases carbon dioxide below 800℃. The mass percentages of quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash are as follows: quicklime 40%, industrial-grade sodium bicarbonate 10%, and secondary aluminum ash 10%. The above components are processed into 5mm spherical particles using a sintering and pelletizing process. The main components of the secondary aluminum ash are as follows: Al2O3: 62.5%, Na2O: 8.2%, CaO: 3.4%, SiO2: 2.4%, MgO: 5.4%, TiO2: 1.70%, SO3: 1.6%, K2O: 1.1%, Fe2O3: 0.5%.

[0030] Example 2

[0031] The difference between Example 2 and Example 1 is that the steel slag crushing agent also includes 5% 80-mesh CaF2 powder. That is, the combination of substances that generate carbon dioxide atmosphere includes: 40% quicklime, 10% industrial grade sodium bicarbonate, 10% secondary aluminum ash, and 5% 80-mesh CaF2 powder. The above components are made into 5 mm spherical particles according to the sintering pelletizing process.

[0032] Example 3

[0033] This invention provides a method for modifying molten steel slag under atmospheric pressure and a carbon dioxide atmosphere throughout the entire process, comprising: throwing 200 kg of the first batch of modified steel slag tailings into a steel slag slag pot; then throwing 22.5% of the mass of the first batch of hot molten steel slag with steel slag shaving agent into the steel slag slag pot; then unloading the second batch of hot molten steel slag into the steel slag slag pot through the slag unloading device of a converter or continuous casting system; then throwing the second batch of hot molten steel slag with 22.5% of the mass of steel slag shaving agent into the steel slag slag pot; and repeating this cycle until the slag pot is full. The steel slag shaving agent is a combination of substances that generate a carbon dioxide atmosphere in stages. Its main components include quicklime, which releases carbon dioxide in the range of 1350-1580℃; industrial-grade sodium bicarbonate, which releases carbon dioxide in the range of 900-1100℃; and secondary aluminum ash, which releases carbon dioxide below 800℃. The mass percentages of quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash are as follows: quicklime 50%, industrial-grade sodium bicarbonate 20%, and secondary aluminum ash 20%. The above components are processed into 10 mm spherical particles using a sintering and pelletizing process. The proportions of the main components in the secondary aluminum ash are as follows: Al2O3: 63.85%, Na2O: 8.6%, CaO: 3.6%, SiO2: 2.6%, MgO: 5.7%, TiO2: 1.825%, SO3: 1.7%, K2O: 1.2%, Fe2O3: 0.54%.

[0034] Example 4

[0035] The difference between Example 4 and Example 3 is that the steel slag crushing agent also includes 7.5% of 115-mesh CaF2 powder. That is, the combination of substances that generate carbon dioxide atmosphere includes: 50% quicklime, 15% industrial grade sodium bicarbonate, 17.5% secondary aluminum ash, and 7.5% 115-mesh CaF2 powder. The above components are made into 10 mm spherical particles according to the sintering pelletizing process.

[0036] Example 5

[0037] This invention provides a method for modifying molten steel slag under atmospheric pressure and carbon dioxide atmosphere throughout the entire process, comprising: throwing 300 kg of the first batch of modified steel slag tailings into a steel slag slag pot; then throwing 35% of the mass of the first batch of hot molten steel slag with steel slag shaving agent into the steel slag slag pot; unloading the second batch of hot molten steel slag into the steel slag slag pot through the slag unloading device of the converter or continuous casting system; then throwing the second batch of hot molten steel slag with 35% of the mass of the second batch of hot molten steel slag with steel slag shaving agent into the steel slag slag pot; and repeating the cycle until the slag pot is full. The steel slag shaving agent is a combination of substances that generate a carbon dioxide atmosphere in stages. Its main components include quicklime, which releases carbon dioxide in the range of 1350-1580℃; industrial-grade sodium bicarbonate, which releases carbon dioxide in the range of 900-1100℃; and secondary aluminum ash, which releases carbon dioxide below 800℃. The mass percentages of quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash are as follows: quicklime 60%, industrial-grade sodium bicarbonate 30%, and secondary aluminum ash 30%. The above components are processed into 15 mm spherical particles according to the sintering and pelletizing process. The proportions of the main components in the secondary aluminum ash are as follows: Al2O3: 65.2%, Na2O: 9.0%, CaO: 3.8%, SiO2: 2.8%, MgO: 5.9%, TiO2: 1.95%, SO3: 1.8%, K2O: 1.3%, Fe2O3: 0.58%.

[0038] Example 6

[0039] The difference between Example 6 and Example 5 is that the steel slag crushing agent also includes 10% of 150-mesh CaF2 powder. That is, the combination of substances that generate carbon dioxide atmosphere includes: 60% quicklime, 20% industrial grade sodium bicarbonate, 25% secondary aluminum ash, and 10% 150-mesh CaF2 powder. The above components are made into 15 mm spherical particles according to the sintering pelletizing process.

[0040] Steel slag crushing agent throwing method as follows Figure 1 The slag crushing agent feeding device system shown includes a conveyor belt 3 with its output end connected to the steel slag hopper 6, a support 1 for supporting the conveyor belt 3, a base 5 for supporting the support 1, and a weighing scale 2 set on one side of the input end of the conveyor belt 3. A monitoring device 4 for monitoring the throwing of steel slag crushing agent on the conveyor belt 3 is set on the support 1 on the output end of the conveyor belt 3.

[0041] Example effect:

[0042] The following is a comparison table of the mass fraction of iron content in the original steel slag, the mass fraction of iron content in the granulated iron particles, and the mass fraction of iron content in the granulated steel slag for each embodiment. As can be seen:

[0043]

[0044] 1. Significantly improves the recovery rate and quality of metallic iron.

[0045] The atmospheric pressure saturated carbon dioxide atmosphere constructed in this invention provides a completely dry, reducing / inert environment for hot molten steel slag, effectively blocking the oxidation reaction of metallic iron with water vapor at high temperatures and avoiding the formation of non-magnetically separable iron oxide or iron hydroxide. Example data shows that this method achieves a recovered iron particle grade as high as 89.6%~92.5%, greatly ensuring the quality of steel resource recovery.

[0046] 2. Optimize the slag-iron separation path to prevent caking and settling.

[0047] By utilizing the continuous disturbance and impact of carbon dioxide gas flow within the slag pot, this invention overcomes the physical inertia of molten iron droplets rapidly settling and agglomerating into large iron lumps during static cooling, ensuring that metallic iron remains discrete from the slag phase throughout the hot cooling process. This dynamic separation mechanism effectively solves the industry problems of easily forming "cup pots" and being difficult to break, such as iron-rich casting residue slag and desulfurization slag, significantly reducing the difficulty of subsequent slag-iron separation.

[0048] 3. Modified steel slag is easy to grind and has high activity, thus multiplying its resource utilization value.

[0049] The steel slag processed by this method exhibits a loose, honeycomb-like porous structure, combining excellent grindability and cementitious activity. The cooled steel slag only requires simple crushing and magnetic separation to achieve separation, and its tailings can be directly used as a high-calcium cement admixture, a high-performance concrete admixture, or a sludge solidification agent, without the need for complex deep processing, significantly broadening the high-value-added utilization pathways of steel slag.

[0050] 4. Eliminate wet processing steps to achieve green and low-carbon production.

[0051] This technology completely eliminates the essential water-cooling and steaming process in traditional methods, thus eliminating the safety hazard of steam explosions at the source, while also avoiding wastewater generation and large-scale dust emissions. This dry modification method not only simplifies the process and reduces energy consumption, but also aligns with the carbon reduction and emission reduction strategies of steel enterprises, achieving safe and ecological steel slag treatment.

[0052] Figure 2 This is a natural cooling curve of molten steel slag in this invention. The curve shows the temperature change pattern of molten steel slag in this invention from a high temperature range of 1350℃ to 1580℃, through a medium temperature range of 900℃ to 1100℃, and then to a low temperature range below 800℃. This temperature range is completely matched with the temperature range of the three-stage temperature zone gas generation and step-by-step dissociation of steel slag by the steel slag crushing agent.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for modifying molten steel slag with carbon dioxide throughout the entire process under normal pressure, characterized in that, include: The first batch of molten steel slag is added to the slag pot for melting. Then, 10%–35% of the first batch of hot molten steel slag by weight of a steel slag shaving agent is added to the slag pot. After the first batch is added, the mixture is allowed to stand for at least 60 minutes. Next, the second batch of hot molten steel slag is unloaded into the slag pot through the slag discharge device of the converter or continuous casting system. Then, 10%–35% of the second batch of hot molten steel slag by weight of a steel slag shaving agent is added to the slag pot. After the second batch is added, the mixture is allowed to stand for at least 60 minutes. The process is repeated until the slag pot is full. The steel slag shaving agent is a combination of substances that generate carbon dioxide atmosphere in stages. Its main components include quicklime that releases carbon dioxide in the range of 1350-1580℃, industrial-grade sodium bicarbonate that releases carbon dioxide in the range of 900-1100℃, and secondary aluminum ash that releases carbon dioxide below 800℃. Through the combination of quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash, a stepped gas release mode is achieved, which includes simultaneous gas production of three components at high temperature, continuous gas production of two components at medium temperature, and stable gas production of one component at low temperature. This provides continuous, stable, and stratified carbon dioxide atmosphere protection throughout the cooling process of steel slag, maximizing the preservation of metallic iron in the steel slag from oxidation, thus enabling its recycling. Furthermore, there are no harmful residues after the quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash supply carbon dioxide. The reaction products can also improve the strength of steel slag and achieve full resource utilization.

2. The method for modifying molten steel slag with carbon dioxide throughout the entire process under normal pressure as described in claim 1, characterized in that, The temperature of the hot-state molten steel slag is in the range of 1350-1580℃. Quicklime, industrial-grade sodium bicarbonate, and secondary aluminum ash decompose simultaneously, releasing carbon dioxide. Quicklime decomposition is dominant, forming a dense gas film on the surface of the molten slag, preventing the molten slag from sticking together. 30-60 minutes after the hot-state molten steel slag is fed, the temperature inside the slag pot drops to 900-1100℃. The quicklime is basically decomposed, while the industrial-grade sodium bicarbonate and secondary aluminum ash continue to decompose and release carbon dioxide, breaking down the internal binding force of the steel slag and achieving loosening and dissociation of the slag body. 60 minutes after the hot-state molten steel slag is fed, the temperature inside the slag pot is below 800℃. Only the secondary aluminum ash continues to release a large amount of carbon dioxide, keeping the steel slag in a loose and non-sticky state in the slag pot for a long time. At the same time, the carbon dioxide gas flow continuously impacts and disturbs the slag body, causing the steel and iron to be fully separated and dispersed from the slag, forming independent steel particles, achieving efficient separation of steel and slag.

3. The method for modifying molten steel slag with carbon dioxide throughout the entire process under normal pressure as described in claim 1, characterized in that, The interval between the two hot-melt steel slag throws should be 30 to 60 minutes, with the optimal interval being 60 minutes.

4. The method for modifying molten steel slag with carbon dioxide throughout the entire process under normal pressure as described in claim 1, characterized in that, The main components of the steel slag crushing agent, by mass percentage, include: quicklime 40%~60%, industrial grade sodium bicarbonate 10%~30%, and secondary aluminum ash 10%~30%. The above components are made into spherical particles of 5~15mm by sintering and pelletizing process.

5. The method for modifying molten steel slag with carbon dioxide at atmospheric pressure as described in claim 1, characterized in that, The main components of the steel slag crushing agent, by mass percentage, include: quicklime 40%~60%, industrial grade sodium bicarbonate 10%~20%, secondary aluminum ash 10%~25%, and 80~150 mesh CaF2 powder 5%~10%. The above components are made into spherical particles of 5~15mm by sintering and pelletizing process.

6. The method for modifying molten steel slag with carbon dioxide at atmospheric pressure as described in claim 1, characterized in that, Secondary aluminum ash is a waste product generated after the remelting of primary aluminum ash or the recycling of aluminum ingots. It has a low aluminum content and its chemical composition by mass percentage is as follows: Al2O3: 62.5~65.2%, Na2O: 8.2~9.0%, CaO: 3.4~3.8%, SiO2: 2.4~2.8%, MgO: 5.4~5.9%, TiO2: 1.70~1.95%, SO3: 1.6~1.8%, K2O: 1.1~1.3%, Fe2O3: 0.5~0.58%.

7. The method for modifying molten steel slag with carbon dioxide at atmospheric pressure as described in any one of claims 1 to 6, characterized in that, The steel slag crushing agent is thrown using a crushing agent feeding device system, which includes a conveyor belt (3) whose output end is connected to the steel slag slag tank (6), a support (1) for supporting the conveyor belt (3), a base (5) for supporting the support (1), and a weighing scale (2) set on one side of the input end of the conveyor belt (3). A monitoring device (4) for monitoring the throwing of steel slag crushing agent on the conveyor belt (3) is set on the support (1) on one side of the output end of the conveyor belt (3).

8. The method for modifying molten steel slag with carbon dioxide at atmospheric pressure as described in claim 7, characterized in that, The modified steel slag has a honeycomb porous structure.

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