Method for densification regulation and full utilization of steel slag

Abstract

The invention relates to a method for fully utilizing steel slag, in particular to a method for regulating and controlling compactness in a steel slag solidification process. Molten steel slag or solid-liquid mixed steel slag with the temperature larger than or equal to 1450 DEG C is used as a treatment object and subjected to thermal crushing and air blowing cooling, and steel slag with the surface temperature ranging from 1200 DEG C to 1350 DEG C is obtained; then carrying out quenching densification treatment until the temperature of the steel slag is reduced to 800-1050 DEG C; during quenching densification treatment, the cooling speed is 200-500 DEG C / min; and then the obtained steel slag is transferred into an annealing and slow-cooling device, the slow-cooling device adopts gas obtained through hot crushing and air blowing cooling for heat compensation, and when the temperature of the steel slag is slowly reduced to 200-300 DEG C, steam generated through quenching densification treatment is introduced for curing. The obtained steel slag is low in porosity, high in density and stability and suitable for industrial application of the steel slag in building materials.

Description

Technical Field

[0001] The present invention relates to a method for fully utilizing steel slag, and in particular to a method for regulating and controlling the density of steel slag during its solidification process and fully utilizing the steel slag. Background Art

[0002] Steel slag is a byproduct of the steelmaking process. China produces over 120 million tons of high-temperature steel slag annually. Currently, the main methods for treating steel slag in my country are hot stuffing and hot pouring, which primarily aim to pulverize the slag and eliminate unstable factors. The treated slag has small particle size, large surface area, and abundant pores. Due to its properties, approximately 25% of this slag is recycled by steel mills or ironworks, for example, as a flux to partially replace CaO in the sintering process or as a source of iron oxide in hot metal pretreatment. Approximately 5% is used in cement production, leaving approximately 70% of the slag unutilized.

[0003] According to the national standard GB175-2023 "General Portland Cement," which will be implemented in 2023, steel slag is not included in the list of primary admixtures permitted for use in general Portland cement production. Since the standard is fully mandatory, this means that steel slag can no longer be used as a regular admixture in general Portland cement production. Against this backdrop, developing high-value utilization options for steel slag beyond micronized cement production is particularly urgent. This groundbreaking technological exploration is of strategic importance in promoting an environmentally friendly, resource-efficient, and sustainable development model for the steel industry.

[0004] Steel slag, rich in silicates and metal oxides, exhibits excellent mechanical properties and durability. Its compressive strength, wear resistance, and chemical stability make it a promising alternative to natural stone, with wide applications in roadbed materials, building blocks, asphalt aggregate, and railway ballast. Currently, my country's annual demand for natural stone for infrastructure construction reaches billions of tons. However, due to strict environmental regulations restricting mining, natural sand and gravel resources are becoming increasingly scarce, and prices are rising. In contrast, developed countries have already made extensive use of steel slag in road construction, with usage rates reaching 32%, 43%, and 50% in Japan, Europe, and the United States, respectively. In my country, the utilization rate of steel slag in road construction is less than 3%, leaving significant market potential for development. However, due to the excessive addition of CaO during steelmaking to ensure desiliconization and dephosphorization, steel slag is prone to forming free calcium oxide (f-CaO) during cooling. This component undergoes significant volume expansion (approximately 200%) upon contact with water, leading to structural cracking and other problems, severely restricting the direct application of steel slag in construction.

[0005] The patent "A High-Strength Steel Slag Board and Its Forming Method" (application number CN202411718856.2) mixes steel slag powder with a silicon extender to create a powder mixture. Water is then added to the powder mixture and stirred to form a mortar mixture. The processed mortar mixture forms a high-strength steel slag board. While this invention improves the strength of steel slag, both the steel slag and the silicon extender are in fine powder form, and the addition of the silicon extender increases processing cost and difficulty. The patent "A Steel Slag Aggregate with Improved Stability of Cement-Steel Slag Concrete, Its Preparation Method, and Application" (application number CN202411580785.4) coats and modifies steel slag aggregate using recycled micropowder and a geopolymer mixture. The resulting coating has a dense three-dimensional interpenetrating network structure that strengthens the slag surface interface and inhibits contact between the internal slag and water. While this invention can enhance aggregate interfacial strength and improve concrete stability, it still requires high particle size for the recycled micropowder and multiple processing steps for the newly formed steel slag. Current inventions for improving the density and stability of steel slag mostly target the reprocessing of already produced cold steel slag. The optimized solution of the present invention is based on high-temperature liquid-solid coexistence steel slag, precisely dividing the temperature range according to its solidification characteristics. Initial solidification and crushing tasks are performed in the high-temperature range. Rapid cooling measures are used in the medium-temperature range to fix the liquid phase and fill the gaps between phases, inhibiting gas retention. In the low-temperature range, slow cooling and stress relief are used to obtain dense steel slag particles, greatly reducing the contact area between the steel slag particles and water, and reducing alkaline leaching. The more efficient and energy-saving stabilization of the steel slag surface expansion factor provides a solution to the low utilization rate of steel slag and the shortage of natural stone resources in my country. Summary of the Invention

[0006] The present invention is to develop and utilize domestic steel slag resources and solve the problem of low steel slag utilization in my country. The existing steel slag pretreatment process pursues a high pulverization rate to improve the stability of the steel slag, and further grinding is required in the subsequent treatment of the steel slag product to recover the metal elements in the slag. However, this steel slag treatment method not only consumes a large amount of energy, but also the application of the steel slag powder remaining after metal recovery is very limited, and the value created is also relatively small. Therefore, the present invention attempts to regulate the steel slag solidification process from the high-temperature stage, utilize the characteristics of the mobile liquid phase that is conducive to filling the pores of the steel slag, and use rapid cooling to stabilize the liquid phase in the homogeneous nucleation stage and before the final mineral phase precipitates, thereby obtaining a final product that expands upon immersion in water and has extremely low porosity.

[0007] The steel slag product obtained by the temperature-controlled steel slag densification treatment method designed in the present invention can fully or partially replace natural stone for use as aggregate in transportation infrastructure construction, reduce the amount of steel slag stockpiles from the root, and alleviate the tense situation in the use of natural stone. It has high research value and application market.

[0008] The optimized design ideas of the present invention are:

[0009] The present invention controls the solidification of high-temperature steel slag at the production site through an integrated design of multi-stage variable speed cooling, thermal crushing, heat energy recovery and resource utilization, with the aim of obtaining steel slag particles with good density.

[0010] After the converter steelmaking process is complete, a large amount of slag is produced. At this point, the slag temperature ranges from 1450°C to 1650°C, and most of it is liquid. This slag is poured into a slag pot. However, to meet the actual production schedule, this portion of slag is not immediately sent to the slag processing workshop. Instead, it waits until the next converter steelmaking cycle is complete before receiving slag. Depending on the converter steelmaking process, the slag pot is naturally cooled for 15–25 minutes. After receiving two or three rounds of converter slag, a crust forms on the surface of the slag and along the pot walls, providing some insulation. The filled slag pot is then transported to the slag processing workshop, where the slag temperature drops to 1450–1550°C. The slag still remains mostly liquid upon arrival.

[0011] Under ideal conditions, rapidly solidifying high-temperature liquid slag using quenching can produce denser slag. This is because at high temperatures, the mineral phase is homogeneously nucleated, resulting in well-shaped, isotropic grains, allowing the liquid phase to effectively fill the gaps between the phases. Currently, water is the most cost-effective quenching medium. However, in practice, high-temperature water quenching has been found to present two challenges. First, large amounts of liquid, high-temperature slag can cause splashing or steam explosions when exposed to water, posing a hazard to personnel and equipment. Second, the quenched slag product exhibits high stress and pulverization. Therefore, selecting the appropriate quenching temperature range, quenching time, and slag volume is crucial for achieving structurally stable and dense slag. First, the slag is poured from the slag pot into a crusher with a closed hood. Low-volume air cooling is used at a relatively slow cooling rate to achieve initial solidification and thermal crushing of the slag. This allows for initial growth of the mineral phase within the slag and allows for the recovery of high-quality, high-temperature gases. The slag temperature is monitored in real time during the crushing process. When the temperature of the slag drops to 1200~1350℃, it is moved to the rapid cooling line. The rapid cooling line uses a large water curtain cooling device equipped with a continuous conveying cooling tank. This step quickly fixes 15%~25% of the liquid phase in the slag, allowing it to effectively fill the existing mineral phase gaps. The temperature of the slag after passing through the water curtain is reduced to 900~1050℃, and it is transferred to the slow cooling device. The slow cooling device uses the high-temperature hot air produced in the thermal crushing stage to supplement heat, and slowly cools it to 200℃~300℃ at a cooling rate of 2-10℃ / min. Then, the steam produced in the rapid cooling process is introduced for curing to reduce stress and improve structural stability. The cooled slag is crushed to obtain slag particles of different particle sizes. Since the surface and interior of the obtained slag particles are relatively dense, the unstable components are tightly wrapped by the solidified mineral phase or liquid phase, effectively reducing their contact area with water, effectively ensuring the long-term stability of the slag particles.

[0012] Preferably, the method of the present invention for controlling and fully utilizing steel slag densification comprises the following steps:

[0013] Step 1

[0014] Molten steel slag or solid-liquid mixed steel slag is used as the processing object, and the slag is thermally crushed and air-cooled to obtain steel slag with a surface temperature of 1200-1350°C; the temperature of the processing object is greater than or equal to 1450°C;

[0015] Step 2

[0016] The steel slag obtained in step 1 and having a surface temperature of 1200-1350° C. is subjected to rapid cooling treatment. The rapid cooling step comprises: transferring the steel slag obtained in step 1 and having a temperature of 1200-1350° C. into a water curtain device for rapid cooling and densification treatment until the temperature of the steel slag drops to 800-1050° C.; during the rapid cooling and densification treatment, the cooling rate is 200-500° C. / min, preferably 300-500° C. / min;

[0017] Step 3

[0018] The steel slag with a temperature of 800-1050°C in step 2 is transferred to an annealing and slow cooling device. The slow solidification device uses the hot air produced in step 1 for supplementary heating. When the temperature of the steel slag slowly decreases to 200-300°C, the steam produced in step 2 is introduced for curing; the slow cooling rate is less than or equal to 15°C / min.

[0019] In step one of the present invention, molten or solid-liquid mixed steel slag is treated, slowly cooled by air blowing and thermally crushed to 1200-1350°C, while high-quality hot gas is recovered. The average cooling rate of the steel slag in step one is controlled to be 10-25°C / min.

[0020] In industrial applications, in step 1, the blown gas is heated to an average temperature of 200-400°C. After heat exchange, the high-temperature gas can be used again to cool the slag, thus recovering the heat from the high-temperature slag.

[0021] In step 1, the molten steel slag comprises, by mass percentage, the following: TFe 10-30%, CaO 30-50%, SiO2 10-50%, MgO 1-10%, Al2O3 1-8%, and P2O5 1-3%. In practical applications, the molten steel slag may contain a small amount of impurities not listed here, which are negligible. In practical applications, the Fe oxide content of the molten steel slag is 10-30% by weight.

[0022] As a preferred step 1, the temperature of the treatment object is 1450-1650°C.

[0023] When used in industry, the molten steel slag in step 1 can be the final slag of converter steelmaking after multiple recycling. Of course, other steel slags with compositions and temperatures that meet the requirements of the present invention can also be used in the present invention.

[0024] In the present invention, step 1 may preferably be:

[0025] Pour the treated object into the crushing bed with a closed cover; after the slag is poured in, close the closed cover and blow 10000Nm 3 / h ~ 40000Nm 3 / h of air and / or nitrogen, and at the same time, the roller crushing device is turned on to crush the steel slag for thermal crushing. After 1 to 3 times of roller crushing, the steel slag particle size is less than 37.5mm, the steel slag temperature is reduced to 1200~1350℃, and the steel slag solidification and granulation time is 5~25min.

[0026] In step 1 of the present invention, the slag is immediately subjected to thermal crushing and blast cooling after being poured out, wherein the thermal crushing is to break up the large crusted slag and lift the liquid slag, and at the same time blow 10000~30000Nm 3 / h of air or nitrogen cools the liquid slag evenly and slowly, promoting the escape of dissolved gases and the growth of mineral phases.

[0027] In the treatment object described in step 1, the liquid phase content is 15wt%~30wt%.

[0028] In step 2 of the present invention, a certain thickness is spread according to the quality of the slag. The slag entering the water curtain is rapidly solidified, and the residual liquid phase fills the gaps between the mineral phases. Under the uniform and rapid cooling of the water curtain, the porosity of the slag is effectively reduced, and the temperature is simultaneously reduced to 800-1050°C.

[0029] In step 2 of the present invention, the steel slag obtained in step 1, with a surface temperature of 1200-1350°C, is rapidly cooled. The rapid cooling process involves transferring the steel slag obtained in step 1, with a temperature of 1200-1350°C, into a water curtain cooling device. The water curtain cooling device is a cooling line equipped with multiple water curtain generators, a continuous feeder, and real-time slag temperature monitoring. After the steel slag enters the water curtain, the water curtain generators are activated to form a uniform water curtain, rapidly cooling the steel slag to a temperature of 800-1050°C while the slag temperature is monitored in real time. During the rapid cooling process, a large amount of steam generated is collected.

[0030] When used in industry, the length of the water curtain is set to 10~15m, the width is 2~3m, and the thickness of the slag laying is 0.1~0.5m according to the quality of the slag.

[0031] Preferably, in step 2, the water curtain cooling time is 45 to 300 seconds, preferably 50 to 75 seconds, so that the slag on the output track is cooled to 800 to 1050°C, preferably 800 to 850°C.

[0032] In step three of the present invention, the slag particles from step two are slowly cooled to eliminate internal stress. The rapidly cooled slag is then transferred to a slow cooling unit equipped with an insulation layer, a temperature monitoring system, and a slag conveying system. This unit provides a heat-insulating environment and slows down the cooling of the slag. This unit uses the high-quality hot air produced in step one to replenish heat within the slow cooling unit, slowing the cooling rate of the slag. Steam produced in step two is also introduced to the slow cooling unit to maintain the stone particles. After cooling to below 100°C, the slag particles are further crushed or screened.

[0033] Preferably, in step 3, the slow cooling rate is preferably 1-8°C / min, so that the slag is slowly cooled to below 100°C. First, the 200-400°C hot gas produced in step 1 is used for supplementary heating. When the slag temperature drops to 200-300°C, the steam produced in step 2 is used for curing to gradually release the stress inside the slag and prevent cracking and structural instability.

[0034] After the treatment in step three, the temperature of the steel slag is reduced to below 100° C., and high-strength steel slag aggregates of different particle sizes can be obtained by screening or further crushing.

[0035] In the present invention, the steel slag particles after densification control have a dense structure, which reduces the contact between unstable factors such as CaO and MgO and water, avoids internal expansion of the steel slag, and effectively improves its stability.

[0036] Through the treatment in step 3, structurally stable and dense steel slag particles can be obtained;

[0037] After the treatment in step three, the temperature of the steel slag particles is reduced to below 100° C., and steel slag particles of different particle sizes are obtained through a screening machine, which can be used in the field of building materials, such as fully or partially replacing natural stone for road construction, concrete coarse aggregate or concrete fine aggregate.

[0038] In the present invention, the recovery rate of heat brought by the molten slag is 20% to 40%.

[0039] The steel slag stone material obtained by this invention has a water expansion rate of 0.20-1.0%, a porosity of 1.5-2.0%, and a crushing value of 10-16, meeting the requirements of the national industry standard YB / T 484-2018. After optimization, the steel slag stone material obtained by this invention has a water expansion rate of 0.20-0.6%, a porosity of 1.5-1.8%, a crushing value of 10-14, and a strength of greater than or equal to 50 MPa. More importantly, the strength of the steel slag stone material obtained by this invention has been significantly improved, reaching a maximum strength of 65 MPa or above.

[0040] Compared with the existing technology, the present invention has the following advantages: Unlike the traditional steel slag treatment process, the present invention pre-treats the final slag of converter steelmaking through high-temperature thermal crushing - medium-temperature water curtain rapid cooling - low-temperature slow cooling, obtains small-particle liquid-containing steel slag through a specific air inlet system combined with roller crushing, and then uses water curtain rapid rapid cooling measures to quickly solidify the liquid phase, avoiding liquid phase exhaustion or the emergence of high-viscosity liquid phase, so that the liquid phase can fully fill the existing mineral phase pores. It reduces the problems of explosiveness and high pulverization caused by direct quenching of large amounts of high-temperature steel slag. Low-temperature slow cooling effectively utilizes the waste heat of high-temperature steel slag, reduces quenching thermal stress, and prevents cracking of steel slag particles. The dense steel slag particles effectively stabilize the volume expansion factors, realizing the complete stoneization of steel slag resources.

[0041] 1. This process proposes a method for regulating and controlling the densification of steel slag. The final product is a highly dense and stable steel slag stone with a strength of no less than 45 MPa. This method can effectively inhibit the hydration reaction of f-CaO and f-MgO in the steel slag. The product can partially or completely replace natural stone in road construction, concrete coarse and fine aggregates, railway ballast and other fields, alleviating the shortage of natural stone and the difficulty in utilizing steel slag.

[0042] 2. The temperature control range of quenched slag and the staged solidification control process are proposed for the first time. The operating equipment can be improved based on the current steel plant slag disposal process of roller crushing-hot stuffing method, with low investment cost, low dust pollution from closed equipment and high product value.

[0043] 3. Recover the waste heat from the high temperature section of steel slag and use it to cure steel slag stone products to eliminate internal stress in the products. No additional heat supply is required throughout the entire treatment process, which is in line with the green transformation concept of the steel industry.

[0044] 4. This invention is expected to break through the "technical bottleneck" of traditional steel slag treatment methods, increase the steel slag utilization rate from 30% to 60%~80%, and realize the metallurgical technology upgrade of full value-added utilization of metallurgical solid waste steel slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a schematic diagram of a method for regulating the density of steel slag according to the present invention.

[0046] Figure 2 This is a microscopic morphology of the steel slag particles obtained in Example 1;

[0047] Figure 3 This is the microscopic morphology of the steel slag particles obtained in Comparative Example 2.

[0048] from Figure 3 It can be seen that the product obtained in Example 1 is dense.

[0049] from Figure 3 It can be seen that the product obtained in Comparative Example 2 has obvious pores. DETAILED DESCRIPTION

[0050] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0051] Example 1:

[0052] The molten steel slag used in this example is converter slag, whose composition, by mass percentage, includes: TFe (total iron) 20.84%, CaO 33.86%, SiO2 21.65%, MgO 3.51%, Al2O3 1.95%, P2O5 2.52%, FeO 26.79%, and the remainder is impurities. The slag basicity is 1.56. After converter steelmaking, the slag is poured into slag pots. Each slag pot receives slag from two batches of converter slag, totaling approximately 30 tons. After slag collection, it enters the slag processing workshop, where the specific operations are as follows:

[0053] (1) The crane carries the slag pot to the roller crushing area, and the overhead crane lifts the slag pot to the slag unloading platform. The crushing area sealing cover is opened, and the automatic tipping device of the slag pot is turned on until the slag is completely poured out. After the slag is poured in, the sealing cover is closed, and the blower and roller crushing device are turned on at the same time. The blast air volume is 30000Nm 3 / h, real-time monitoring of slag temperature changes. When the slag particle size is less than 37.5mm and the temperature drops to 1200℃ (the average cooling rate of this process is about 20℃ / min), the slag is transported to the water curtain rapid cooling zone via a heat-resistant conveyor belt, and the temperature is raised to 350℃ after gas heat exchange.

[0054] (2) After crushing, the steel slag at about 1200°C enters the water curtain cooling device. The thickness of the steel slag particles is 0.3m, and the length of the water curtain cooling zone is 10m. The granular steel slag after the water curtain quickly completes the final solidification (the water curtain cooling time is 60 seconds). The steel slag particles after rapid cooling are transported out along the conveyor belt. At this time, the steel slag temperature is about 800°C. A large amount of water vapor generated during the rapid cooling process is collected. The average cooling rate of this process is 400°C / min.

[0055] (3) After the 800℃ steel slag particles enter the low-temperature slow cooling zone, the 350℃ hot air collected when cooling the steel slag in the high-temperature section is introduced for supplementary heat. The steel slag is controlled to slowly cool to 200℃, and then steam curing is introduced until the steel slag is cooled to below 100℃. The average cooling rate of this process is 2℃ / min.

[0056] (4) The treated steel slag is vibrated and screened to obtain steel slag stone of different particle sizes. The dense and stable steel slag finally obtained can be used as a substitute for natural stone aggregate, realizing the full conversion of steel slag into stone. The microscopic morphology of steel slag is shown in the figure below. Figure 2 The water expansion rate of steel slag stone is 0.2%, the porosity is 1.5%, the crushing value is 12, and the strength is 65MPa, which meets the requirements of the national industry standard YB / T484-2018.

[0057] Example 2:

[0058] The steel slag used in this example is converter slag, whose composition, by mass percentage, includes: TFe 20.46%, CaO 41.58%, SiO 13.17%, MgO 8.80%, Al 2 O 3 1.71%, P 2 O 5 2.49%, FeO 26.31%, with the remainder being impurities. The slag basicity is 3.16. After converter steelmaking, the slag is poured into slag pots. Each slag pot receives slag from three furnaces of converter slag, for a total of approximately 40 tons. After receiving the slag, it enters the slag processing workshop. The difference from Example 1 lies in the different quality and composition of the slag received in the slag pots. The specific operation is as follows:

[0059] (1) The crane carries the slag pot to the roller crushing area, and the overhead crane lifts the slag pot to the slag unloading platform. The crushing area sealing cover is opened, and the automatic tipping device of the slag pot is turned on until the slag is completely poured out. After the slag is poured in, the sealing cover is closed, and the blower and roller crushing device are turned on at the same time. The blast air volume is 40000Nm 3 / h, real-time detection of slag temperature changes. When the slag particle size is less than 37.5mm and the temperature drops to 1350℃, the average cooling rate of this process is about 15℃ / min. The slag is transported to the water curtain rapid cooling zone through a heat-resistant conveyor belt. The gas is heated to 400℃ after heat exchange.

[0060] (2) After crushing, the steel slag at about 1350℃ enters the water curtain cooling device. The accumulation thickness of the steel slag particles is 0.4m, and the length of the water curtain cooling zone is 10m. The granular steel slag after the water curtain quickly completes the final solidification. The steel slag particles after rapid cooling are transported out along the conveyor belt. At this time, the steel slag temperature is about 1000℃. A large amount of water vapor generated during the rapid cooling process is collected. The average cooling rate of this process is 350℃ / min.

[0061] (3) After the 1000℃ steel slag particles enter the low-temperature slow cooling zone, the 400℃ hot air collected when cooling the steel slag in the high-temperature section is introduced for supplementary heat, and the steel slag is controlled to slowly cool to 200℃. Then, steam curing is introduced until the steel slag temperature drops below 100℃. The average cooling rate of this process is 1.7℃ / min.

[0062] (4) The treated steel slag is vibrated and screened to obtain steel slag stone of different particle sizes. The resulting dense and stable steel slag can be used as a substitute for natural stone aggregate, achieving full steel slag stoneification. The steel slag stone has a water expansion rate of 0.5%, a porosity of 1.8%, a crushing value of 14, and a strength of 50 MPa, meeting the requirements of the national industry standard YB / T 484-2018.

[0063] Example 3:

[0064] The steel slag used in this example is converter slag, whose composition, by mass percentage, includes: TFe 17.30%, CaO 41.55%, SiO 18.04%, MgO 4.02%, Al 2 O 3 7.96%, P 2 O 5 2.71%, FeO 22.25%, and the remainder is impurities. The slag basicity is 2.30. After converter steelmaking, the slag is poured into slag pots. Each slag pot receives slag from three batches of converter slag, totaling approximately 40 tons. After receiving the slag, it enters the slag processing workshop. The difference from Example 1 lies in the different quality and composition of the slag received in the slag pots. The specific operation is as follows:

[0065] (1) The crane carries the slag pot to the roller crushing area, and the overhead crane lifts the slag pot to the slag unloading platform. The crushing area sealing cover is opened, and the automatic tipping device of the slag pot is turned on until the slag is completely poured out. After the slag is poured in, the sealing cover is closed, and the blower and roller crushing device are turned on at the same time. The blast air volume is 40000Nm 3 / h, real-time detection of slag temperature changes, after the slag particle size is reduced to 37.5mm and the temperature is reduced to 1300℃, the average cooling rate of this process is about 16℃ / min, the slag is transported to the water curtain rapid cooling zone through a heat-resistant conveyor belt, and hot air with a temperature of 400℃ can be obtained at the same time;

[0066] (2) After crushing, the steel slag at about 1300℃ enters the water curtain cooling device. The accumulation thickness of the steel slag particles is 0.40m, and the length of the water curtain cooling zone is 10m. The granular steel slag after the water curtain quickly completes the final solidification. The steel slag particles after rapid cooling are transported out along the conveyor belt. At this time, the steel slag temperature is about 1000℃, and the average cooling rate of this process is 300℃ / min.

[0067] (3) After the 1000℃ steel slag particles enter the low-temperature slow cooling zone, the hot air collected when cooling the steel slag in the high-temperature section is introduced for supplementary heat, and the steel slag is controlled to slowly cool to 200℃. Then, steam curing is introduced until the steel slag temperature drops below 100℃. The average cooling rate of this process is 1.7℃ / min.

[0068] (4) The treated steel slag is vibrated and screened to obtain steel slag stone of different particle sizes. The resulting dense and stable steel slag can be used as a substitute for natural stone aggregate, achieving full conversion of steel slag into stone. The steel slag stone has a water expansion rate of 0.4%, a porosity of 1.6%, a crushing value of 13, and a strength of 55 MPa, meeting the requirements of the national industry standard YB / T 484-2018.

[0069] Comparative Example 1:

[0070] This comparative example is essentially the same as Example 2, except that the high-temperature slag is directly water-cooled without undergoing high-temperature crushing. The high-temperature slag produces a large amount of steam during the quenching process, resulting in a pulverization rate of approximately 70% for the resulting slag product. This means that the slag product is mostly small particles or slag powder less than 10 mm in diameter, and further pulverizes during long-term storage. The resulting product exhibits a water expansion rate of 2.8%, a porosity of 5%, a crushing value of 28, and a strength of 30 MPa, which do not meet the requirements for slag aggregates in the national industry standard YB / T 484-2018.

[0071] Comparative Example 2: This comparative example is basically the same as Example 2, except that the temperature of the slag before entering the water curtain is 800°C. Since the slag has completely solidified, with the solidification and shrinkage of the final mineral phase and the retention of gas inside the slag, a large number of pores have appeared inside the slag. At this time, further water curtain rapid cooling will basically not change the composition of the pores. The cross-sectional micromorphology is as follows: Figure 3 The obtained product has a water expansion rate of 3.2%, a porosity of 6.5%, a crushing value of 30, and a strength of 25 MPa, which does not meet the requirements for steel slag aggregates in the national industry standard YB / T 484-2018.

[0072] Comparative Example 3: This comparative example is essentially the same as Example 2, except that no slow cooling stress relief or steam curing treatment was performed. Specifically, the water-curtain-cooled slag particles were not transferred to the slow cooling unit but instead stored for natural cooling. During the cooling process, the slag particles exhibited varying degrees of pulverization and cracking, resulting in long-term structural instability. The resulting product exhibited a water expansion ratio of approximately 1.8%, a porosity of approximately 4%, a crushing strength of approximately 25, and a strength of approximately 40 MPa, failing to meet the requirements for slag aggregates in the national industry standard YB / T 484-2018.

[0073] Comparative Example 4

[0074] Other conditions are the same as those in Example 2, except that:

[0075] (2) After crushing, the steel slag at about 1200°C enters the water curtain cooling device. The thickness of the steel slag particles is 0.3m, and the length of the water curtain cooling zone is 10m. The granular steel slag after the water curtain completes the final solidification (the water curtain cooling time is 240 seconds). The steel slag particles after rapid cooling are transported out along the conveyor belt. At this time, the steel slag temperature is about 800°C. A large amount of water vapor generated during the rapid cooling process is collected. The average cooling rate of this process is 100°C / min.

[0076] (3) After the 800℃ steel slag particles enter the low-temperature slow cooling zone, the cooling rate is controlled at 10℃ / min.

[0077] The obtained product has a water expansion rate of about 2%, a porosity of about 5%, a crushing force of about 26, and a strength of about 40 MPa, which does not meet the requirements for steel slag aggregates in the national industry standard YB / T 484-2018.

Claims

1. A method for densification control and full utilization of steel slag, characterized in that: The steps include: Step 1 Molten steel slag or solid-liquid mixed steel slag is used as the processing object, and the slag is thermally crushed and air-cooled to obtain steel slag with a surface temperature of 1200-1350°C; the temperature of the processing object is greater than or equal to 1450°C; Step 2 The steel slag obtained in step 1 and having a surface temperature of 1200-1350° C. is subjected to rapid cooling treatment. The rapid cooling step comprises: transferring the steel slag obtained in step 1 and having a temperature of 1200-1350° C. into a water curtain device for rapid cooling and densification treatment until the temperature of the steel slag drops to 800-1050° C.; during the rapid cooling and densification treatment, the cooling rate is 200-500° C. / min, preferably 300-500° C. / min; Step 3 The steel slag with a temperature of 800-1050°C in step 2 is transferred to an annealing and slow cooling device. The slow solidification device uses the hot air produced in step 1 for supplementary heating. When the temperature of the steel slag slowly decreases to 200-300°C, the steam produced in step 2 is introduced for curing; the slow cooling rate is less than or equal to 15°C / min.

2. The method for controlling and fully utilizing steel slag densification according to claim 1, characterized in that: In step one, molten or solid-liquid mixed steel slag is treated by air blowing, slowly cooling it and thermally crushing it to 1200-1350°C, while simultaneously recovering high-quality hot gas. The average cooling rate of the steel slag in step one is controlled at 10-25°C / min.

3. The method for controlling and fully utilizing steel slag densification according to claim 1, characterized in that: In step 1, the blown gas is heated to an average temperature of 200-400°C, and the high-temperature gas is used again to cool the slag after heat exchange.

4. The method for controlling and fully utilizing steel slag densification according to claim 1, characterized in that: In step 1, the molten steel slag comprises, by mass percentage, TFe 10-30%, CaO 30-50%, SiO2 10-50%, MgO 1-10%, Al2O3 1-8%, and P2O5 1-3%.

5. The method for controlling and fully utilizing steel slag densification according to claim 1, characterized in that: In step 1, the temperature of the treatment object is 1450~1650℃.

6. The method for controlling and fully utilizing steel slag densification according to claim 1, characterized in that: Step one can be: Pour the treated object into the crushing bed with a closed cover; after the slag is poured in, close the closed cover and blow 10000Nm 3 / h ~ 40000Nm 3 / h air and / or nitrogen, and at the same time, open the roller crushing device to crush the steel slag for thermal crushing. After 1 to 3 roller crushings, the steel slag particle size is less than 37.5mm, the steel slag temperature is reduced to 1200~1350℃, and the steel slag crushing time is 5~25min; In the treatment object described in step 1, the liquid phase content is 15wt%~30wt%.

7. The method for controlling and fully utilizing steel slag densification according to claim 1, characterized in that: In step 2, the water curtain cooling time is 45 to 300 seconds, preferably 50 to 75 seconds, so that the slag on the output track is cooled to 800 to 1050°C, preferably 800 to 850°C.

8. The method for controlling and fully utilizing steel slag densification according to claim 1, characterized in that: In step 3, the slow cooling rate is preferably 1-8°C / min, so that the slag is slowly cooled to below 100°C.

9. The method for controlling and fully utilizing steel slag densification according to claim 1, characterized in that: The obtained steel slag stone has a water expansion rate of 0.20-1.0%, a porosity of 1.5-2.0%, and a crushing value of 10-16; after optimization, the steel slag stone obtained by the present invention has a water expansion rate of 0.20-0.6%, a porosity of 1.5-1.8%, a crushing value of 10-14, and a strength of greater than or equal to 50 MPa.

10. The method for controlling and fully utilizing steel slag densification according to claim 1, characterized in that: After the treatment in step three, the temperature of the steel slag particles is reduced to below 100°C, and steel slag particles of different particle sizes are obtained through a screening machine and used in the field of building materials.

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