Method for setting the steam aging treatment period for crushed steelmaking slag, and steam aging treatment method.

Abstract

This invention provides a method for setting the steam aging treatment period for steelmaking slag crushed stone and a steam aging treatment method using this method, which ensures that the criteria for water immersion expansion ratio are always satisfied, even when the basicity and crushed stone particle size differ, and that subsequent reprocessing can be avoided. [Solution] The required treatment period T for steam aging of steelmaking slag crushed stone is determined by the product of the coefficient E0, which represents the expansion characteristics based on the basicity (CaO / SiO2) of the steelmaking slag, and the square of the maximum radius R of the crushed stone, T = E0R 2 The formula is used for calculation. When the basicity of steelmaking slag is less than 2, E0 = 0.05; when the basicity is between 2 and 3, E0 = 0.2; and when the basicity exceeds 3, E0 = 0.7. In addition, the maximum radius R of the crushed stone can be determined according to the JIS standard.

Description

Technical Field

[0001] The present invention relates to the steam aging treatment of steelmaking slag crushed stone, and specifically to a treatment technique for specifying the shortest period (required treatment period) required for the steam aging treatment of steelmaking slag crushed stone.

Background Art

[0002] The cooled and crushed steelmaking slag is hard and can be used as a roadbed material for roads. However, the slag crushed stone immediately after crushing contains unreacted lime (in the form of free lime) inside. Therefore, when used as a roadbed material, it reacts with moisture such as rainwater and expands in volume by about twice that of unreacted lime, which may cause abnormalities (such as unevenness and cracks) in the road surface. Therefore, it is necessary to carry out an aging treatment before use to terminate this hydration reaction.

[0003] In JIS-A-5015 (Steelmaking Slag for Road), which is Non-Patent Document 1, an air aging method and an accelerated aging method (steam aging method) are defined as aging treatment methods for steelmaking slag crushed stone. Air aging is a method in which the crushed steelmaking slag crushed stone is piled up in the atmosphere for 6 months or more to cause a hydration reaction between free lime and rainwater, etc., and to stabilize the expansibility. However, this method requires a very long period for the aging treatment, requires a large area of land, has poor treatment efficiency, and there is a problem that the variation in the progress of the stabilization of the expansibility in the piled-up steelmaking slag crushed stone is large.

[0004] Therefore, as a solution to this problem, an accelerated aging method (steam aging method) has been developed and is currently the mainstream. Hereinafter, this method will be simply referred to as the steam aging method. As this steam aging method, the method described in Non-Patent Document 2 is common. Specifically, it is a method in which a pile of steelmaking slag crushed stone is surrounded by a retaining wall, and steam is blown in from a pipe installed below it.

[0005] JIS-A-5015 explicitly states that the atmospheric aging treatment period should be at least six months. However, regarding steam aging, it only states that "the aging period can be shortened by confirming that the expansion properties have stabilized sufficiently, based on construction experience, etc.," and does not specify a concrete aging period. In other words, there are no official standards or guidelines for the steam aging treatment period. In reality, the departments that manufacture steelmaking slag crushed stone determine the treatment period through trial and error, and there is no industry-wide standardized treatment period. Therefore, in order to manufacture and use new steelmaking slag as road base material, trial and error must be repeated each time. And if the expansion properties have not decreased sufficiently, the steam aging treatment must be performed again.

[0006] Furthermore, the water immersion expansion test is the common method for evaluating the expansion characteristics of steel slag roadbed material, including steelmaking slag. Annex 2 of the aforementioned JIS-A-5015 specifies the method for water immersion expansion testing of steel slag. Specifically, the steel slag is held at 80°C for 6 hours, and then allowed to cool in the apparatus, repeating this process once a day for 10 days. According to the current JIS-A-5015 (2018 edition), the standard for shipping steel slag roadbed material is that the water immersion expansion ratio in this test must be 1.0% or less. Based on these existing manufacturing technologies and methods for evaluating expansion characteristics, the steam aging treatment period was determined through trial and error, and there was no unified approach or uniform setting method.

[0007] Furthermore, even with the same steelmaking slag, the expansion suppression effect due to steam aging differs between coarse-grained and fine-grained slags, and it is recognized that the expansion suppression effect differs depending on the type of steelmaking slag even if the particle size is the same. For this reason, if the water immersion expansion ratio cannot be cleared to 1.0% or less in the evaluation test of expansion characteristics after steam aging treatment, it has been proposed to perform atmospheric aging treatment with additional moisture, as shown in Patent Document 1. Such trial-and-error steam aging treatment methods are costly and time-consuming, and a solution has been sought. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] JIS-A-5015 "Steelmaking slag for roads" (2018 edition) [Non-Patent Document 2] Sasaki et al., "Development of Steam Aging Treatment for Steelmaking Slag," Nippon Steel & Sumitomo Metal Technical Report, No. 399 (2014), pp. 21-25. [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2017-7880 [Overview of the project] [Problems that the invention aims to solve]

[0010] Therefore, the object of the present invention is to solve the above-mentioned conventional problems and to provide a method for setting the steam aging treatment period for steelmaking slag and a steam aging treatment method using this method, which ensures that any steelmaking slag and any crushed stone particle size satisfies the standard for water immersion expansion ratio and avoids subsequent reprocessing. [Means for solving the problem]

[0011] The inventors of this invention investigated the relationship between the steam aging treatment period and the water immersion expansion ratio after treatment for various types of crushed steel slag. As a result, they found that the water immersion expansion ratio is greatly influenced by the maximum particle size of the crushed stone and the basicity of the steel slag. Furthermore, the influence of the particle size of the crushed stone on the hydration reaction rate during steam aging treatment was also analyzed based on the unreacted nucleus model described later. This invention was made based on the above findings.

[0012] In other words, the method for setting the steam aging treatment period for crushed steelmaking slag according to the present invention is to set the required treatment period T for steam aging treatment of crushed steelmaking slag by the product of a coefficient E0 that shows the expansion characteristics based on the basicity (CaO / SiO2) of the steelmaking slag and the square of the maximum radius R of the crushed stone, which is T = E0R 2 It is characterized by being calculated using the following formula.

[0013] Furthermore, it is preferable to set E0 = 0.05 when the basicity of the steelmaking slag is less than 2, E0 = 0.2 when the basicity is between 2 and 3, and E0 = 0.7 when the basicity exceeds 3.

[0014] Furthermore, it is preferable that the maximum radius R of the crushed stone be (26.5 / 2) mm for CS-20, which has a standard particle size range of 20 to 0 mm; (37.5 / 2) mm for CS-30, which has a standard particle size range of 30 to 0 mm; and (53 / 2) mm for CS-40, which has a standard particle size range of 40 to 0 mm.

[0015] Furthermore, the steam aging treatment method for steelmaking slag crushed stone of the present invention is characterized by calculating the required treatment period T (hours) for the steam aging treatment of steelmaking slag crushed stone using the following formula (1), and performing steam aging treatment for the calculated required treatment period T. T=E0R 2 ...(1) Here, E0 = 0.05 when the basicity of steelmaking slag is less than 2, E0 = 0.2 when the basicity is 2 or more and 3 or less, and E0 = 0.7 when the basicity is greater than 3. For CS-20, where the standard particle size range of crushed stone is 20 to 0 mm, R = (26.5 / 2) mm, for CS-30, where the standard particle size range is 30 to 0 mm, (37.5 / 2) mm, and for CS-40, where the standard particle size range is 40 to 0 mm, (53 / 2) mm. [Effects of the Invention]

[0016] According to the present invention, it is possible to perform steam aging treatment on any steelmaking slag and any crushed stone particle size, ensuring that the water immersion expansion ratio standard is always satisfied and avoiding subsequent reprocessing.

Brief Description of the Drawings

[0017] [Figure 1] It is an explanatory diagram of the "unreacted core model". [Figure 2] It is a logarithmic graph showing the required treatment period of steam aging according to basicity and particle size. [Figure 3] It is a histogram showing the distribution of water expansion ratio before steam aging treatment. [Figure 4] It is a histogram showing the distribution of water expansion ratio after 5 days of steam aging treatment. [Figure 5] It is a histogram showing the distribution of water expansion ratio after 6 days of steam aging treatment.

Modes for Carrying Out the Invention

[0018] Embodiments of the present invention will be described below. First, the logic underlying the present invention will be described. The expansion of steelmaking slag crushed stone is mainly caused by the hydration reaction in which free lime (free lime) in the slag reacts with surrounding moisture and is represented by the formula CaO + H2O ⇒ Ca(OH)2. It is said that this digestion reaction causes a volume expansion of about twice the volume of CaO alone. That is, if 5% of free lime is contained, the average volume expansion ratio is approximately 5%. Since the standard for the water immersion expansion ratio of roadbed materials specified in the aforementioned JIS is 1% or less, it is presumed that the concentration of free lime has a great influence. In general, as the basicity (CaO / SiO2) in the slag composition increases, the concentration of free lime in the slag rapidly increases, so the water immersion expansion ratio of steelmaking slag also increases. Therefore, it is presumed that the water immersion expansion ratio after steam aging is a function of basicity.

[0019] Also, although it has been empirically known that the particle size of steelmaking slag crushed stone affects the required treatment period of steam aging, there has been no clear calculation formula in the past, so trial and error has been repeated. As a result of the analysis based on the "unreacted core model" described below by the present inventor, the relationship between the particle size of the crushed stone and the required treatment period of steam aging has been clarified.

[0020] Figure 1 is an explanatory diagram of the "unreacted nucleus model." In this model, the crushed steelmaking slag is considered a sphere of radius R, and it is assumed that gaseous components (water vapor) diffuse onto the particle surface through a gas boundary film formed on the surface of the solid particles (outer surface of the particles) during steam aging, reacting with the unreacted portion of the solid particles to form a layer of solid reaction products around a central nucleus. The reaction surface moves toward the center of the sphere over time, and a layer of solid reaction products gradually forms outside the reaction surface, while the inside of the reaction surface remains unreacted. This reaction proceeds over time, but it is assumed that the particle size (radius R) of the crushed steelmaking slag is kept constant.

[0021] This reaction proceeds through the following steps. (1) Gas-phase component A diffuses to the particle surface through the gas boundary film. (2) Gas-phase component A diffuses through the layer of solid reaction products to the interface of the unreacted portion. (3) The solid on the reaction surface reacts with gaseous component A. These three processes occur in series, with the slowest being the rate-determining process. In the steam aging process, (1) and (3) proceed rapidly, and (2) becomes the rate-determining process. Since the diffusion phenomenon is based on Maxwell's partial differential equations, the reaction completion time can be expressed by the following equation based on the results of these analyses. T∝R 2 , or T = A / D × R 2 Here, A is a constant and D is the diffusion coefficient. As shown in the above equation, the reaction time between crushed slag and steam during steam aging is proportional to the square of the radius of the crushed slag.

[0022] Based on the above analysis, we discovered that the required treatment period for steam aging of crushed steelmaking slag can be derived from the product of the coefficient E0, which represents the expansion characteristics determined by the basicity of the slag, and the square of the radius of the largest particle size of the crushed steelmaking slag. Based on this concept, using a vast amount of data from on-site operation data and water immersion expansion ratios, we determined T=E0R 2 We constructed a specific estimation formula for this.

[0023] In this formula, R is the radius of the largest particle size of crushed stone. In the aforementioned JIS standard, crushed and sieved steelmaking slag is classified into three categories based on particle size range: CS-20, CS-30, and CS-40. The standard particle size range for CS-20 is 0 to 20 mm, with a maximum particle size of 26.5 mm. Similarly, the standard particle size range for CS-30 is 0 to 30 mm, with a maximum particle size of 37.5 mm, and the standard particle size range for CS-40 is 0 to 40 mm, with a maximum particle size of 53 mm. Therefore, in this formula, the radii of the largest particle size of crushed stone in the three categories of crushed stone (CS-20, CS-30, and CS-40) are set to 26.5 / 2 mm, 37.5 / 2 mm, and 53 / 2 mm, respectively.

[0024] In this formula, the coefficient E0, which indicates the expansion characteristic, was set as follows: E0 = 0.05 when the basicity (CaO / SiO2) is less than 2, E0 = 0.2 when the basicity is between 2 and 3, and E0 = 0.7 when the basicity is greater than 3. The unit is time / mm 2 That is the case.

[0025] Table 1 shows the required steam aging period calculated based on this formula. Figure 2 shows a log-log graph of the number of days (required treatment period) for steam aging treatment by basicity and particle size.

[0026] [Table 1]

[0027] As shown in Table 1, even for steelmaking slags with the same basicity, the steam aging treatment period is greatly affected by the particle size, with CS-30 requiring approximately twice the treatment period of CS-20, and CS-40 requiring approximately four times the treatment period of CS-20. The basicity of the steelmaking slag also has a significant impact; when the basicity exceeds 3, there is a particularly large amount of free lime, raising concerns about quality abnormalities due to volume expansion, thus requiring a long steam aging treatment. Specifically, high-basicity slag requires approximately 14 times the treatment period compared to low-basicity slag. By performing steam aging treatment for the required treatment period T calculated in this way, the standard for water immersion expansion ratio can be guaranteed to be met for any steelmaking slag and any crushed stone particle size, thus avoiding subsequent reprocessing. [Examples]

[0028] Example 1 is an example of applying the present invention to converter slag (CS-20) with very high basicity. Converter slag, a type of steelmaking slag, has a basicity of 3-8 and is classified as a high-basicity slag. The water immersion expansion ratio of steelmaking slag immediately after crushing is 3-6%, which is significantly outside the JIS standard. Furthermore, when the water immersion expansion ratio of crushed stone made from this steelmaking slag was measured, the average was 3.66%, as shown in the histogram in Figure 3, which does not meet the JIS standard. Note that each rectangle in Figure 3 represents one lot.

[0029] Therefore, in accordance with JIS standards, a steam aging treatment was performed for one week, and as shown in the graph in Figure 4, the average water immersion expansion ratio drastically decreased to 0.76%. However, when examining the individual data after the steam aging treatment, some data did not satisfy the JIS standard of a water immersion expansion ratio of 1.0% or less, meaning that not all units passed the test. For this reason, some lots required further steam aging treatment.

[0030] Therefore, when we performed another week of steam aging on lots that did not meet the JIS standard of a water immersion expansion ratio of 1.0% or less, we were able to satisfy that standard. However, repeating the steam aging process increased steam costs and product handling, resulting in delays in shipping. For this reason, this operational method of repeatedly performing steam aging and measuring the water immersion expansion ratio presented many challenges in terms of production management, yield, manufacturing costs, and delivery to customers.

[0031] Previously, steam aging treatment was performed in one cycle, or one week. Specifically, one day was used for slag loading and one day for steam aging equipment inspection, so the net duration of the steam aging treatment was based on five days. Therefore, additional steam aging treatments were also performed in one-week increments as described above, with a net treatment period of five days.

[0032] On the other hand, when the required treatment period T for steam aging treatment was calculated using the present invention, it was found to be 5.12 days. Since the net treatment period for the first steam aging treatment was 5 days, it was confirmed that this was slightly insufficient. Therefore, when the net treatment period for the first steam aging treatment was extended from 5 days to 6 days, as shown in Figure 5, it was confirmed that all lots satisfied the JIS standard of a water immersion expansion ratio of 1.0% or less, and there was no need for re-treatment with steam aging. [Examples]

[0033] Example 2 is an example of applying the present invention to low-basicity slag (CS-20 and CS-40) with a basicity of less than 2. According to the present invention, the required treatment period T for steam aging treatment was calculated to be 0.37 days for CS-20 and 1.46 days for CS-40. Therefore, the steam aging treatment period for CS-20 was shortened to 1 day, and the steam aging treatment period for CS-40 was shortened to 2 days. The water immersion expansion ratio after steam aging treatment was 0.05% for CS-20 and 0.17% for CS-40. Despite the significant reduction in the steam aging treatment period compared to conventional methods, it was confirmed that the water immersion expansion ratio after treatment met the JIS standard for both.

[0034] Thus, with both CS-20 and CS-40, the water immersion expansion ratio could be kept within JIS standards, eliminating the need for reprocessing and significantly shortening the processing time. As a result, it became possible to produce road base materials according to plan, unlike the previous method which involved repeated trial and error, eliminating shipping delays and leading to smoother sales.

[0035] As explained above, according to the present invention, it is possible to estimate the appropriate steam aging treatment period based on the basicity of the steelmaking slag and the maximum particle size (radius) of the crushed slag, thereby avoiding deviations from the standard water immersion expansion ratio after aging treatment due to insufficient aging. Therefore, it becomes possible to smoothly and systematically proceed with the stable production and shipment of crushed steelmaking slag, and to minimize the cost of steam aging treatment. Thus, the practical value of the present invention is extremely high.

Claims

1. The required treatment period T for steam aging of steelmaking slag crushed stone is defined as T = E0R, which is the product of the expansion coefficient E0, which is based on the basicity of the steelmaking slag, and the square of the maximum radius R of the crushed stone. ２ A method for setting the steam aging treatment period for crushed steelmaking slag, characterized by calculating it using the following formula.

2. A method for setting the steam aging treatment period for crushed steelmaking slag according to claim 1, wherein E0 = 0.05 when the basicity of the steelmaking slag is less than 2, E0 = 0.2 when the basicity is 2 or more and 3 or less, and E0 = 0.7 when the basicity is greater than 3.

3. A method for setting the steam aging treatment period for steelmaking slag crushed stone according to claim 1 or 2, wherein the maximum radius R of the crushed stone is set to (26.5 / 2) mm in the case of CS-20 with a standard particle size range of 20 to 0 mm, to (37.5 / 2) mm in the case of CS-30 with a standard particle size range of 30 to 0 mm, and to (53 / 2) mm in the case of CS-40 with a standard particle size range of 40 to 0 mm.

4. A method for steam aging crushed steel slag, characterized by calculating the required treatment period T (hours) for steam aging of the crushed steel slag using the following formula (1), and performing steam aging for the calculated required treatment period T. T=E0R ２ ・・・(1) Here, E0 = 0.05 when the basicity of steelmaking slag is less than 2, E0 = 0.2 when the basicity is 2 or more and 3 or less, and E0 = 0.7 when the basicity is greater than 3. For CS-20, where the standard particle size range of crushed stone is 20 to 0 mm, R = (26.5 / 2) mm, for CS-30, where the standard particle size range is 30 to 0 mm, (37.5 / 2) mm, and for CS-40, where the standard particle size range is 40 to 0 mm, (53 / 2) mm.

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