A method for reducing the content of free calcium oxide in fresh steel slag in a low-carbon and environment-friendly manner

Abstract

This invention discloses a low-carbon and environmentally friendly method for reducing the free calcium oxide content in freshly produced steel slag, comprising the following steps: 1) crushing the freshly produced steel slag in a jaw crusher to obtain steel slag with various particle size ranges; 2) mixing the steel slag with various particle size ranges according to a set method, and then transporting them in batches to sealed compartments in the plant for stacking; 3) allowing the slag to naturally age for a set time in the sealed compartments to obtain steel slag with a free calcium oxide content meeting the set requirements. This invention utilizes water vapor and carbon dioxide in the air to chemically modify the steel slag, reducing its free calcium oxide content and improving its chemical stability.

Description

Technical Field

[0001] This invention belongs to the field of steel slag treatment methods, and more specifically, relates to a low-carbon and environmentally friendly method for reducing the free calcium oxide content in freshly produced steel slag. Background Technology

[0002] Steel slag is a byproduct of steelmaking. Due to the enormous demand for steel in fields such as construction, aviation, and machinery, a large amount of steel slag is generated during iron ore refining. At the end of 2022, my country's annual crude steel output was 1.018 billion tons, with annual steel slag production exceeding 150 million tons, and the total stockpiled amount is increasing year by year. The large-scale stockpiling of steel slag not only wastes land resources but also potentially causes environmental pollution, posing a significant challenge to environmental protection.

[0003] The main chemical components of steel slag are CaO, SiO2, Al2O3, and MgO. Due to its poor stability, steel slag develops cracks and bulges after several years of use, hindering its widespread application. Extensive research has revealed that the primary cause of its poor volume stability is the high content of free calcium oxide in the steel slag. High free calcium oxide content is one of the main problems affecting the resource utilization rate of steel slag and a long-standing challenge for the steel industry. Therefore, there is an urgent need to research technologies to reduce the free calcium oxide content of steel slag and improve its resource utilization rate.

[0004] There are precedents in China for research on reducing the free calcium oxide content in steel slag. CN115872637A discloses a method for reducing free calcium oxide in steel slag. By introducing carbon dioxide during the steam curing process of steel slag, the content of free calcium oxide in steel slag is reduced, the stability of steel slag is improved, and the utilization rate of steel slag is increased.

[0005] CN101851071A discloses a method for carbon dioxide fixation and the elimination of free calcium oxide in steel slag powder. This method utilizes CO2 from waste flue gas to chemically modify the steel slag powder, reducing the content of free calcium oxide and improving its chemical stability. CN114292039A relates to a method for reprocessing steel slag for asphalt concrete. This method involves pre-laying steel slag flat at the bottom of a hot curing tank and controlling the temperature, humidity, pressure, and water spray volume to reduce the content of free calcium oxide. These methods are complex to operate and consume significant human and material resources. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a low-carbon and environmentally friendly method for reducing the free calcium oxide content of freshly produced steel slag. The method adopts natural aging, which can greatly reduce the energy consumption of mechanization. During the aging process, carbon dioxide in the atmosphere can be absorbed, reducing the free calcium oxide content of steel slag, thus having a certain positive impact on the environment.

[0007] To achieve the above objectives, according to the present invention, a low-carbon and environmentally friendly method for reducing the free calcium oxide content in freshly produced steel slag is provided, characterized by comprising the following steps:

[0008] 1) Freshly produced steel slag is put into a jaw crusher for crushing to obtain steel slag with a variety of particle size ranges;

[0009] 2) After mixing steel slag of various particle sizes according to the set method, the mixture is transported in batches to the sealed compartments of the plant for stacking.

[0010] 3) After natural aging in a sealed compartment for a set time, steel slag with a free calcium oxide content that meets the set requirements can be obtained.

[0011] Preferably, the relative humidity threshold for each sealed compartment is 60%-80%, the pressure threshold for each sealed compartment is 0.7MPa-1.2MPa, and the temperature threshold for each sealed compartment is 25℃-40℃. Lower humidity prevents water vapor in the air from fully contacting the free calcium oxide on the steel slag surface, while higher humidity causes water vapor to corrode the steel slag surface, altering its physicochemical properties. Lower pressure and temperature prevent the free calcium oxide in the steel slag from fully reacting with water vapor and nitrogen dioxide in the air, but higher pressure and temperature lead to greater resource consumption.

[0012] Preferably, the steel slag obtained by the jaw crusher has four particle size ranges: less than 5mm, 5-10mm, 10-20mm, and greater than 20mm.

[0013] Preferably, steel slag of various particle size ranges is mixed according to a mass percentage, and the mass percentages of steel slag of different particle size ranges in each sealed compartment are as follows:

[0014] The mass percentage of steel slag with a particle size of less than 5 mm is 30% to 36%.

[0015] The mass percentage of steel slag with a particle size of 5-10 mm is 25% to 30%.

[0016] The mass percentage of steel slag with a particle size of 10-20 mm is 22% to 26%.

[0017] The mass percentage of steel slag with a particle size greater than 20 mm is 15% to 18%.

[0018] Furthermore, within each sealed compartment, the sum of the percentages of steel slag in these particle size ranges is 100%.

[0019] This combination of particle size range and ratio ensures that steel slag of various sizes can fully contact the air, which helps to reduce free calcium oxide.

[0020] Preferably, freshly produced steel slag refers to slag produced within a time interval of no more than 720 minutes between the pouring of molten steel from the steelmaking furnace and its placement in the jaw crusher.

[0021] Preferably, the factory building is a closed rectangular factory building, which is divided into different sealed compartments by partition walls.

[0022] Preferably, the partition wall is a cement concrete retaining wall.

[0023] Preferably, the steel slag is piled in N layers, where N≥3, and from bottom to top are layer 1, layer 2, ..., layer N. Each layer has multiple steel slag piles to form a long strip, and the laying method is as follows:

[0024] 1) First, many isosceles triangular piles of steel slag are laid in the first layer, that is, the bottom layer;

[0025] 2) Each slag heap in the j-th layer is rhomboid, and each slag heap in the j-th layer is located between two adjacent slag heaps in the (j-1)-th layer, where j = 2, 3…N-1;

[0026] 3) The Nth layer, or top layer, consists of many inverted isosceles triangular piles of steel slag, with a flat top. Each pile in the Nth layer is located between two adjacent piles in the (N-1)th layer. This arrangement makes the steel slag piles more stable and less prone to collapse. It also creates gaps between the steel slag in the same layer and between different layers, allowing for sufficient contact with air and helping to reduce free calcium oxide.

[0027] Preferably, the slag is stored in each sealed compartment for six months to two years. Too short a aging time will prevent the free calcium oxide in the slag from fully reacting with water vapor and carbon dioxide in the air. Once the free calcium oxide has fully reacted with the water vapor and carbon dioxide, extending the storage time will not have a positive effect on reducing the free calcium oxide content, but will greatly increase resource consumption and reduce the effective floor space occupied.

[0028] Preferably, the steel slag is stacked using a belt conveyor with an unloading trolley. The belt conveyor can move up, down, forward, backward, and rotate horizontally. These movements can be accomplished by combining a rotary table and a two-dimensional motion platform mounted on the rotary table.

[0029] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0030] (1) The present invention selects a suitable method for stacking fresh steel slag, and uses water vapor and carbon dioxide in the air to chemically modify the steel slag, reduce its free calcium oxide content, and improve the chemical stability of the steel slag.

[0031] (2) This invention reduces the free calcium oxide content of steel slag through natural aging. During the aging process, the steel slag can absorb carbon dioxide from the atmosphere, achieving carbon reduction and negative carbon, which has a certain positive impact on the environment.

[0032] (3) This invention can promote the aging of steel slag in a high-temperature and humid environment. It utilizes water vapor and carbon dioxide in the air to chemically modify the steel slag, reduce its free calcium oxide content, and improve the chemical stability of the steel slag. By improving the stacking method of steel slag, the efficiency of steel slag aging is improved, the turnover rate of natural aging stockpiles is increased, and the safety of steel slag in concrete and mortar applications is enhanced.

[0033] (4) The method and process used in this invention are relatively simple and low in cost, making it suitable for widespread application. Attached Figure Description

[0034] Figure 1 This is a simplified top view of the factory building according to an embodiment of the present invention.

[0035] In the diagram, 1-factory gate, 2-sealed compartment, 3-steel slag pile, 4-factory passageway, 5-retaining wall. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0037] In the following embodiments, the steel slag raw material used was provided by Guangxi Liuzhou Iron and Steel Group Co., Ltd. The plant has a main gate 1 and sealed compartments 2. Each sealed compartment is used to store steel slag piles 3. There are plant passageways 4 inside the plant. The sealed compartments 2 are separated by retaining walls 5.

[0038] Example 1

[0039] First, the freshly produced steel slag from Liuzhou Steel Plant is crushed in a large jaw crusher to obtain four types of steel slag with particle sizes of less than 5mm, 5-10mm, 10-20mm, and greater than 20mm. The four types of steel slag with different particle sizes are then mixed according to the following mass percentage:

[0040] Less than 5mm 5-10mm 10-20mm >20mm 30％ 30％ 22％ 15％

[0041] The mixed steel slag is placed on a conveyor belt equipped with a discharge trolley and promptly pushed into the plant. The environment of the sealed compartments within the enclosed rectangular plant (relative humidity 60%, pressure 0.7 MPa in each compartment, and temperature threshold of 25°C in each compartment) is computer-controlled to ensure optimal conditions for steel slag storage. The plant is divided into different storage areas by partition walls. The mixed steel slag is stacked in these sealed compartments. During stacking, the material is first laid in a layer of parallel isosceles triangular strips, then a second layer is laid between these triangular strips, forming a rhombus shape. This process is repeated, with subsequent rhomboid layers added one after another. Finally, the steel slag is stacked into a square, with a flat top. It can be used after six months of storage.

[0042] Example 2

[0043] First, freshly produced steel slag from Liugang Steel Plant is taken into a large jaw crusher for crushing to obtain four types of steel slag with particle sizes of less than 5mm, 5-10mm, 10-20mm and greater than 20mm. The four types of steel slag with different particle sizes are then mixed according to their mass percentages.

[0044] Less than 5mm 5-10mm 10-20mm >20mm 33％ 27％ 24％ 16％

[0045] The mixed steel slag is placed on a conveyor belt equipped with a discharge trolley and promptly pushed into the plant. The environment of the sealed compartments within the enclosed rectangular plant (relative humidity 70%, pressure 1.1 MPa in each compartment, and temperature threshold of 32°C in each compartment) is computer-controlled to ensure optimal conditions for steel slag storage. The plant is divided into different storage areas by partition walls. The mixed steel slag is stacked in these sealed compartments. During stacking, the material is first laid in a layer of parallel isosceles triangular strips, then a second layer is laid between these triangular strips, forming a rhombus shape. This process is repeated, with subsequent rhomboid layers added one at a time. Finally, the steel slag is stacked into a square, with a flat top. It can be used after one year of storage.

[0046] Example 3

[0047] First, freshly produced steel slag from Liugang Steel Plant is taken into a large jaw crusher for crushing to obtain four types of steel slag with particle sizes of less than 5mm, 5-10mm, 10-20mm and greater than 20mm. The four types of steel slag with different particle sizes are then mixed according to their mass percentages.

[0048] Less than 5mm 5-10mm 10-20mm >20mm 36％ 25％ 22％ 18％

[0049] The mixed steel slag is placed on a belt conveyor equipped with a discharge trolley and promptly pushed into the plant. The environment of the sealed compartments within the enclosed rectangular plant (relative humidity 80%, pressure 1.2 MPa in each compartment, and temperature threshold of 40°C in each compartment) is computer-controlled to ensure optimal conditions for steel slag storage. The plant is divided into different storage areas by partition walls. The mixed steel slag is stacked in these sealed compartments. During stacking, the material is first laid in a layer of parallel isosceles triangular strips, then a second layer is laid between these triangular strips, forming a rhombus shape. This process is repeated, with subsequent rhomboid layers added one after another. Finally, the steel slag is stacked into a square, with a flat top. It can be used after two years of storage.

[0050] Comparative Example 1

[0051] First, freshly produced steel slag from Liugang Steel Plant is taken into a large jaw crusher for crushing to obtain four types of steel slag with particle sizes of less than 5mm, 5-10mm, 10-20mm and greater than 20mm. The four types of steel slag with different particle sizes are then mixed according to their mass percentages.

[0052] Less than 5mm 5-10mm 10-20mm >20mm 36％ 30％ 22％ 15％

[0053] The mixed steel slag is placed on a conveyor belt equipped with an unloading trolley and promptly pushed into the plant. The plant is not enclosed, and the internal environment is determined by real-time weather conditions. The plant is divided into different storage areas by partition walls. The mixed steel slag is stacked in different sealed compartments. During stacking, the material is first laid in a bottom layer of many parallel isosceles triangular strips, then a second layer is laid between the triangular strips, forming a rhombus shape. This process is repeated, with subsequent rhomboid layers added one after another. Finally, the steel slag is stacked into a square, with a flat top. It can be used after six months of storage.

[0054] Comparative Example 2

[0055] First, freshly produced steel slag from Liugang Steel Plant is taken into a large jaw crusher for crushing to obtain four types of steel slag with particle sizes of less than 5mm, 5-10mm, 10-20mm and greater than 20mm. The four types of steel slag with different particle sizes are then mixed according to their mass percentages.

[0056] Less than 5mm 5-10mm 10-20mm >20mm 33％ 27％ 24％ 16％

[0057] The mixed steel slag is placed on a conveyor belt equipped with an unloading trolley and promptly pushed into the plant. The plant is not enclosed, and the internal environment is determined by real-time weather conditions. The plant is divided into different storage areas by partition walls. The mixed steel slag is stacked in different sealed compartments. During stacking, the material is first laid in a bottom layer of many parallel isosceles triangular strips, then a second layer is laid between the triangular strips, forming a rhombus shape. This process is repeated, with subsequent rhomboid layers added one after another. Finally, the steel slag is stacked into a square, with a flat top. It can be used after one year of storage.

[0058] Comparative Example 3

[0059] First, freshly produced steel slag from Liugang Steel Plant is taken into a large jaw crusher for crushing to obtain four types of steel slag with particle sizes of less than 5mm, 5-10mm, 10-20mm and greater than 20mm. The four types of steel slag with different particle sizes are then mixed according to their mass percentages.

[0060]

[0061]

[0062] The mixed steel slag is placed on a conveyor belt equipped with an unloading trolley and promptly pushed into the plant. The plant is not enclosed, and the internal environment is determined by real-time weather conditions. The plant is divided into different storage areas by partition walls. The mixed steel slag is stacked in different sealed compartments. During stacking, the material is first laid in a bottom layer of many parallel isosceles triangular strips, then a second layer is laid between the triangular strips, forming a rhombus shape. This process is repeated, with subsequent rhomboid layers added one after another. Finally, the steel slag is stacked into a square, with a flat top. It can be used after two years of storage.

[0063] The free calcium oxide content of the steel slag obtained in Examples 1-3 and Comparative Examples 1-3 was tested using the glycerol-ethanol method. Freshly produced, unaged steel slag was used as a blank group. The specific test results are shown in Table 1.

[0064] Table 1. Test results of free calcium oxide content in the steel slag after aging in Examples 1-3 and Comparative Examples 1-3.

[0065]

[0066] The above results show that, by using the fresh steel slag stacking method described in this invention, the free calcium oxide content of the steel slag obtained in Examples 2 and 3 is significantly reduced, and the technical indicators meet the requirements of road surface specifications.

[0067] This is achieved by using water vapor and carbon dioxide from the air to chemically modify the steel slag, reducing its free calcium oxide content. By improving the stockpiling method of the steel slag, the efficiency of steel slag aging is enhanced, and the turnover rate of natural aging stockpiles is increased.

[0068] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-carbon and environmentally friendly method for reducing the free calcium oxide content in freshly produced steel slag, characterized in that, Includes the following steps: 1) Freshly produced steel slag is placed into a jaw crusher for crushing to obtain steel slag with various particle size ranges. Freshly produced steel slag refers to steel slag from the time the molten steel is poured out of the steelmaking furnace to the time the slag is placed into the jaw crusher, which is no more than 720 minutes. The particle size range of steel slag obtained by jaw crusher is below 5mm, 5-10mm, 10-20mm and above 20mm. 2) Steel slag of various particle size ranges is mixed according to a set method and then transported in batches to sealed compartments in the plant for stacking. The threshold values ​​for relative humidity in each sealed compartment are 60%-80%, pressure in each sealed compartment are 0.7 MPa-1.2 MPa, and temperature in each sealed compartment are 25℃-40℃. The steel slag of various particle size ranges is mixed according to mass percentage. The mass percentages of steel slag of different particle size ranges in each sealed compartment are as follows: The mass percentage of steel slag with a particle size of less than 5 mm is 30%~36%; The mass percentage of steel slag with a particle size of 5-10 mm is 25%~30%; The mass percentage of steel slag with a particle size of 10-20mm is 22%~26%; The mass percentage of steel slag with a particle size greater than 20 mm is 15%~18%; Furthermore, within each sealed compartment, the sum of the percentages of steel slag within these particle size ranges is 100%. 3) After natural aging in a sealed compartment for a set period of time, steel slag with a free calcium oxide content that meets the set requirements can be obtained. The steel slag is stored in each sealed compartment for a period of six months to two years.

2. The method for reducing the free calcium oxide content in freshly produced steel slag in a low-carbon and environmentally friendly manner according to claim 1, characterized in that, The factory building is a closed rectangular building, which is divided into different sealed compartments by partition walls.

3. The method for reducing the free calcium oxide content in freshly produced steel slag in a low-carbon and environmentally friendly manner according to claim 2, characterized in that, The partition wall is a cement concrete retaining wall.

4. The method for reducing the free calcium oxide content in freshly produced steel slag in a low-carbon and environmentally friendly manner according to claim 1, characterized in that, The steel slag is piled in N layers, where N≥3, and from bottom to top are layer 1, layer 2, ..., layer N. Each layer has multiple steel slag piles to form a long strip of material, and the laying method is as follows: 1) First, lay many isosceles triangular piles of steel slag in the first layer, that is, the bottom layer; 2) Each slag heap in the j-th layer is rhomboid, and each slag heap in the j-th layer is located between two adjacent slag heaps in the (j-1)-th layer, where j = 2, 3…N-1; 3) The Nth layer, which is also the top layer, is filled with many inverted isosceles triangular piles of steel slag, and the top is flat. Each pile of steel slag in the Nth layer is located between two adjacent piles of steel slag in the N-1th layer.

5. The method for reducing the free calcium oxide content in freshly produced steel slag in a low-carbon and environmentally friendly manner according to claim 1, characterized in that, The steel slag is stacked using a belt conveyor with a discharge trolley. The belt conveyor can move up, down, forward, backward, and rotate horizontally.

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