Method for managing slag and method for producing slag material

Abstract

To provide a method for managing a slag capable of controlling an increase in a processing cost of the slag, and to provide a method for producing a slag material.SOLUTION: A method for managing a slag includes: an estimation step of estimating a maximum free lime content in a slag generated by refining, based on a component composition of a secondary raw material to be used in refining molten iron and a Si concentration of molten iron before refining; a first determination step of determining whether or not the maximum free lime content of the slag estimated in the estimation step is a predetermined first threshold value or more; and a decision step of deciding a processing method for the slag based on a result determined in the first determination step.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for managing slag and a method for producing slag material. [Background technology]

[0002] For example, in the steel industry, slag is a by-product of the operation of blast furnaces, pretreatment processes, converters, electric furnaces, etc. Among these slags, the slag produced as a by-product in the steelmaking process, such as the pretreatment process, converters, and electric furnaces, is specifically called steelmaking slag. In the steelmaking process, a large amount of lime is added as an auxiliary material to remove phosphorus, silicon, and other substances contained in the molten iron. As a result, undissolved lime and lime that crystallizes during cooling remain in the steelmaking slag as free lime (hereinafter, free lime may be referred to as "f-CaO").

[0003] This f-CaO has the property of expanding in volume by approximately two times when it becomes Ca(OH)2 through hydration. Therefore, when steelmaking slag containing a large amount of f-CaO comes into contact with water, the slag expands and collapses due to the hydration reaction of f-CaO. One application of steelmaking slag is as roadbed material, but when steelmaking slag containing f-CaO is used as roadbed material, a problem occurs in that the hydration expansion of f-CaO causes the roadbed to bulge.

[0004] For this reason, when steelmaking slag is used as a roadbed material, it is necessary to carry out a pre-treatment such as steam aging on the steelmaking slag, as disclosed in Patent Document 1. Steam aging is a process in which the f-CaO contained in the steelmaking slag is converted to Ca(OH)2 by a hydration reaction to stabilize it. Steam aging is carried out by piling the steelmaking slag in a dedicated treatment plant and flowing steam from the bottom. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-12053 Summary of the Invention [Problem to be solved by the invention]

[0006] For slag containing a large amount of f-CaO, it is difficult to completely eliminate the expansion and collapse property even if steam aging is performed. Conventionally, f-CaO analysis was performed on all slag, and the necessity of steam aging and the steam aging conditions were determined according to the f-CaO content of the slag. This method had the problem of increasing the cost of slag processing because the f-CaO analysis, which is a heavy workload, is performed on a huge number of slags.

[0007] The present invention has been made in consideration of the problems of the conventional technology, and its purpose is to provide a slag management method and a slag material manufacturing method that can suppress an increase in slag processing costs. [Means for solving the problem]

[0008] The means for solving the above problems are as follows. [1] A slag management method comprising: an estimation step of estimating a maximum free lime content contained in slag generated in the refining of molten iron from the component composition of auxiliary materials used in the refining of molten iron and the Si concentration of the molten iron before the refining; a first determination step of determining whether the maximum free lime content of the slag estimated in the estimation step is equal to or greater than a predetermined first threshold value; and a determination step of determining a method for treating the slag based on the result determined in the first determination step. [2] The slag management method according to [1], wherein in the estimation step, T.CaO and T.SiO2 are calculated from the Si concentrations of the auxiliary materials and the molten iron before refining, and the maximum free lime content is estimated using the T.CaO and T.SiO2. [3] A slag management method according to [2], in which the estimation step estimates the maximum free lime content of the slag using the following equation (1). Maximum free lime content = T.CaO-1.86×T.SiO2 (1) [4] A slag management method described in any of [1] to [3], comprising an analysis step of analyzing the free lime content of slag determined to be equal to or greater than the first threshold in the first judgment step, and a second judgment step of determining whether the free lime content analyzed in the analysis step is equal to or greater than a predetermined second threshold, wherein in the determination step, a method for treating the slag is determined based on the results determined in the first judgment step and the second judgment step. [5] A slag management method according to any one of [1] to [3], wherein the first threshold value is 15 kg / t-molten iron. [6] A slag management method as described in [4], in which, in the determination step, it is decided that slag whose free lime content is determined to be equal to or greater than the second threshold value in the second judgment step will not be subjected to steam aging treatment. [7] A method for producing a slag material, comprising treating the slag with a treatment method determined in a determination step in a slag management method described in any one of [1] to [6] to produce a slag material. Effect of the Invention

[0009] According to the present invention, the maximum free lime content of slag generated in the refining of molten iron is estimated, and the estimated maximum free lime content is judged using a first threshold value. This judgment result makes it possible to grasp slag that may have a high f-CaO content and slag that has a low f-CaO content, so that the f-CaO analysis that was conventionally performed for slag with a low f-CaO content can be omitted, thereby suppressing an increase in slag processing costs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be specifically described below through the embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited to these embodiments.

[0011] The slag management method according to the present embodiment includes an estimation step of estimating the maximum free lime content (kg / t-molten iron) of slag generated in the refining from the Si concentration in the molten iron before refining and the auxiliary materials used in the refining of molten iron in a converter, a first judgment step of judging whether the maximum free lime content of the slag estimated in the estimation step is equal to or greater than a first threshold value determined in advance, and a determination step of deciding a slag treatment method based on the result of the judgment in the first judgment step. Each step in the slag management method according to the present embodiment will be described below. In the present embodiment, "molten iron" means molten pig iron and molten steel.

[0012] <Estimated process> First, the estimation process will be described. In the estimation process, the maximum free lime content of the slag generated in each refining of molten iron is estimated. The maximum free lime content of the slag is estimated using the component composition of the auxiliary materials used in refining the molten iron, the input amount of the auxiliary materials, the Si concentration in the molten iron, and the charged amount of the molten iron. Specifically, the maximum free lime content of the slag is estimated by calculating T.CaO (kg / t-molten iron) and T.SiO2 (kg / t-molten iron) using the component composition of the auxiliary materials, the input amount of the auxiliary materials, the Si concentration in the molten iron, and the charged amount of the molten iron. Note that T.CaO is the total lime amount (total lime amount), and T.SiO2 is the total silica amount (total silica amount).

[0013] T.CaO includes not only CaO contained in the auxiliary materials, but also CaCO3, Ca(OH)2, CaMg(CO3)2, etc., which can be converted to CaO by thermal decomposition in high-temperature slag, and T.CaO is calculated assuming that all of these substances are converted to CaO by reactions in the slag. T.SiO2 is calculated assuming that not only SiO2 contained in the auxiliary materials, but also Si in the molten iron and Si in the auxiliary materials are all oxidized to SiO2. The composition of the auxiliary materials, the amount of the auxiliary materials charged, the Si concentration in the molten iron, and the amount of molten iron charged used in the calculation of T.CaO and T.SiO2 may be values ​​used in the refining design of the converter, and it is preferable to estimate the maximum free lime content of the slag using these values ​​at the end of the refining process when the charging of the auxiliary materials to the converter is completed.

[0014] When the CaO in the slag solidifies, it reacts with SiO2 to produce a stable crystal phase represented by 2CaO·SiO2. Therefore, the f-CaO content of the slag can be calculated by subtracting the amount of CaO that has reacted with SiO2 and other substances to stabilize it from the T.CaO.

[0015] CaO forms stable crystal phases with CaO not only with SiO2 but also with P2O5, Al2O3, and Fe2O3. In addition, in the refining of molten iron using a converter, in addition to the slag components formed by the oxidation of auxiliary materials and molten iron components, there is also brought-in slag whose composition and amount are unknown, such as the slag from the previous charge in the converter and the slag attached to the molten iron ladle. Therefore, the true content of f-CaO in the slag is calculated by subtracting not only the SiO2 derived from Si contained in the molten iron, but also the oxide components such as P2O5 and the CaO stabilized by reacting with SiO2 in the brought-in slag from T.CaO. However, since P2O5, Al2O3, and Fe2O3 contained in the slag are not derived from auxiliary materials, it is difficult to grasp the amount of contamination from known information. In addition, since the amount and composition of brought-in slag are unknown, it is also difficult to grasp the amount of SiO2 derived from brought-in slag.

[0016] If the true f-CaO content could be calculated taking into account oxide components such as P2O5 contained in the slag and SiO2 contained in the brought-in slag, the true f-CaO content would be less than the maximum free lime content calculated as above. In other words, the maximum free lime content calculated from the above T.CaO and T.SiO2 would be the maximum f-CaO content that could remain unstabilized in the slag, i.e., the maximum free lime content.

[0017] The maximum free lime content may be theoretically estimated from the stoichiometry of 2CaO SiO2 as shown in the following formula (1). This makes it possible to estimate the maximum free lime content in the slag generated during the refining of molten iron.

[0018] Maximum free lime content (kg / t-molten iron)=T.CaO(kg / t-molten iron)-1.86×T.SiO2(kg / t-molten iron)...(1) In the above formula (1), T.CaO is the CaO and CaCO 3、 This is the total amount of lime (kg / t-molten iron) obtained by converting Ca(OH)2 and CaMg(CO3)2 to CaO, and T.SiO2 is the total amount of silica (kg / t-molten iron) calculated by adding up the SiO2 contained in the auxiliary materials and the SiO2 generated by the oxidation of Si contained in the molten iron. Also, the coefficient 1.86 in the above formula (1) is calculated stoichiometrically from the molecular weights of CaO and SiO2 in 2CaO SiO2.

[0019] As described above, in this embodiment, the f-CaO content when it is assumed that the largest amount of f-CaO remains is estimated as the "maximum free lime content" by the above calculation using T.CaO and T.SiO2, that is, the f-CaO content when the amount of P2O5, Al2O3, Fe2O3, and SiO2 from the carried-in slag, which are difficult to estimate, are set to zero. By estimating this maximum free lime content, it becomes possible to predict the risk that the f-CaO content of the slag generated in the refining of molten iron will be high. In other words, by estimating this maximum free lime content, it becomes possible to specify slag with a low f-CaO content that passes the expansion test with one steam aging treatment.

[0020] <First determination step> Next, the first judgment step will be described. In the first judgment step, it is judged whether the maximum free lime content of the slag estimated in the estimation step is equal to or greater than a first threshold value that is determined in advance for each refining of molten iron. The first threshold value can be set using operational data of the refining of molten iron carried out in the past, for example, by the following steps (1) to (3). (1) The maximum free lime content is estimated from the information on auxiliary raw materials and molten iron for the refining operation data from past slag analysis. (2) The maximum free lime content is identified so that the probability that the amount of free lime will be equal to or greater than the f-CaO content (8% by mass in this embodiment) at which the expansion test will not pass after one steam aging treatment is, for example, 20%. (3) The identified content is set as the first threshold value.

[0021] In order to increase the number of slags to be steam aged without analyzing the content of f-CaO, which will be described later, it is preferable to set the first threshold value as large as possible. On the other hand, if the first threshold value is set too large, there is a concern that a large amount of slag that does not pass the expansion test in one steam aging process will be included. The first threshold value may be set in consideration of this balance, for example, 15 (kg / t-molten iron).

[0022] When the first determination step is performed using the first threshold value set as described above, slag determined to have a maximum free lime content equal to or greater than the first threshold value is slag that may not pass the expansion test in one steam aging treatment, whereas slag determined to have a maximum free lime content less than the first threshold value is slag that will definitely pass the expansion test in one steam aging treatment.

[0023] <Decision process> Next, the determination step will be described. Slag determined to be equal to or greater than the first threshold in the first determination step is slag that may not pass the expansion test with one steam aging treatment. Since it is necessary to analyze the f-CaO content of such slag and perform a re-determination, in the determination step, the slag is determined to be the slag whose f-CaO content is to be analyzed. On the other hand, slag determined to be less than the first threshold in the first determination step is slag that will definitely pass the expansion test with one steam aging treatment. Therefore, in the determination step, such slag is determined to be the slag to be subjected to steam aging treatment without analyzing the f-CaO content.

[0024] By determining the slag treatment method in this way, it becomes possible to perform steam aging treatment on slag without analyzing the f-CaO content and without increasing the risk of not passing the expansion test with one steam aging treatment. As a result, it becomes possible to manufacture slag material that does not expand due to hydration while suppressing increases in slag treatment costs. The expansion test is measured using the test method specified in Appendix B of JIS A5015:2018.

[0025] Moreover, the slag management method according to the present embodiment preferably includes an analysis step of analyzing the f-CaO content of the slag that may not pass the expansion test after one steam aging treatment in the first judgment step. It is also preferable to include a second judgment step of judging whether the f-CaO content analyzed in the analysis step is equal to or greater than a second threshold value determined in advance. In the determination step, it is preferable to determine a slag treatment method based on the results of the first and second judgment steps. Each step will be described below.

[0026] <Analysis process> First, the analysis step will be described. In the analysis step, the f-CaO content of the slag determined in the first determination step to have a maximum free lime content equal to or greater than the first threshold is analyzed. In the analysis step, the slag is sampled from the converter or a transport vessel when the converter slag is discharged or when the converter slag is transported, and the f-CaO content of the slag is analyzed by chemical analysis using, for example, an ethylene glycol extraction method.

[0027] <Second judgment step> Next, the second judgment step will be described. In the second judgment step, it is judged whether the content of f-CaO in the slag analyzed in the analysis step is equal to or greater than a second threshold value that is determined in advance. The second threshold value can be set using actual data on the slag, for example, by the following steps (1) to (3). (1) Slags with different f-CaO contents are prepared, and steam aging treatment and expansion tests are carried out on a laboratory scale. (2) Identify the upper limit of the f-CaO content at which all expansion tests pass after one steam aging treatment (96 hours). (3) The identified upper limit value is set as the second threshold value.

[0028] In order to reduce the number of slags that are used for purposes other than roadbed materials without steam aging, as described below, it is preferable to set the second threshold value as large as possible within the range. On the other hand, if the second threshold value is set too large, there is a concern that slags that do not pass the expansion test after one steam aging treatment will be included. The second threshold value is, for example, 8 mass%.

[0029] When the second judgment step is performed using the second threshold value set as described above, slag whose f-CaO content is judged to be equal to or greater than the second threshold value is slag that does not pass the expansion test after one steam aging treatment, whereas slag whose f-CaO content is judged to be less than the second threshold value is slag that passes the expansion test after one steam aging treatment.

[0030] <Decision process> Slag that is determined to be equal to or greater than the first threshold in the first determination step and equal to or greater than the second threshold in the second determination step is slag that does not pass the expansion test with a single steam aging treatment. In order to prevent the hydration expansion of such slag, a long period of time or multiple steam aging treatments are required, which increases the cost of treating the slag. For this reason, in the determination step, it is preferable to determine not to perform steam aging treatment on such slag and to use the slag material for purposes other than roadbed material where hydration expansion is not a problem.

[0031] On the other hand, slag that is determined to be equal to or greater than the first threshold in the first determination step and equal to or less than the second threshold in the second determination step is slag that passes the expansion test with one steam aging treatment. Therefore, in the determination step, it is preferable to determine that this slag is to be subjected to steam aging treatment, and to use the slag material after the steam aging treatment as a roadbed material. This makes it possible to manufacture slag material that does not expand due to hydration while suppressing increases in slag processing costs.

[0032] In this way, the slag management method according to the present embodiment preferably further includes an analysis step and a second judgment step, and in the determination step, the slag treatment method is preferably determined as described above based on the results of the first and second judgment steps. This makes it possible to determine whether or not aging treatment is required depending on the analysis result of the f-CaO content, and to avoid a situation in which the expansion test is not passed by one steam aging treatment and the steam aging treatment is performed multiple times, thereby further suppressing the increase in the slag treatment cost.

[0033] In the above embodiment, an example is shown in which an analysis step is performed to analyze the f-CaO content for slag determined to be equal to or greater than the first threshold value in the first determination step, but the present invention is not limited to this. Since slag determined to be equal to or greater than the first threshold value in the first determination step is slag that may not pass the expansion test with one steam aging treatment, it may be decided not to perform steam aging treatment on all of the slag, and the slag material may be used for purposes other than roadbed material in which hydration expansion is not a problem.

[0034] In the above embodiment, it is determined that the slag determined to be equal to or greater than the second threshold value in the second judgment step is not to be steam aged, and the slag material is used for purposes other than roadbed materials where hydration expansion is not a problem, but the present invention is not limited to this. It may be determined that the aging time of the steam aging is 1.5 to 2.0 times longer for the slag determined to be equal to or greater than the second threshold value in the second judgment step. This allows the transportation cost to be reduced compared to the case where the slag does not pass the expansion test and is steam aged again, thereby suppressing an increase in the processing cost of the slag. EXAMPLES

[0035] Next, the present invention will be specifically described based on an example. In this example, the slag management method according to this embodiment was applied to slag generated in the decarburization refining of hot metal using a converter. First, the analytical values ​​of the CaO content and SiO2 content in the auxiliary materials used in the decarburization refining, and the analytical value and charging amount of the Si concentration of the hot metal were grasped. Then, at the time when the charging of the auxiliary materials in the decarburization refining of the converter was completed, the estimation process was performed, and T.CaO and T.SiO2 were calculated using the charging amount of the auxiliary materials, the CaO concentration and SiO2 concentration in the auxiliary materials, the Si concentration of the hot metal, and the charging amount of the hot metal, and the maximum free lime content of the slag generated by the decarburization refining was estimated using these values ​​and the above formula (1). Note that T.SiO2 was calculated assuming that the entire amount of Si contained in the hot metal becomes SiO2 by oxidation.

[0036] In the invention examples 1 and 2, the first judgment step was carried out using "maximum free lime content: 10 kg / t-molten iron (invention example 1)" and "maximum free lime content: 15 kg / t-molten iron (invention example 2)" as the first threshold value for the estimated maximum free lime content. In both invention examples 1 and 2, the analysis step of analyzing the f-CaO content of the slag was carried out for the slag whose maximum free lime content was determined to be equal to or greater than the first threshold value in the first judgment step. The aging treatment was carried out for the slag whose maximum free lime content was determined to be less than the first threshold value in the first judgment step without carrying out the analysis step. On the other hand, in the comparative examples 1 and 2, the first judgment step was not carried out, and the analysis step was carried out for all the slags.

[0037] In the analysis process, the free lime content of the slag was analyzed. To analyze the free lime content, 50g of slag was sampled from the slag pot using a metal rod and quickly cooled. After cooling to room temperature, it was crushed and the free lime content of the slag was analyzed by chemical analysis using the ethylene glycol extraction method.

[0038] In the invention examples 1 and 2, the second judgment step was carried out on the slag that had been subjected to the analysis step. In the invention examples 1 and 2, the second judgment step was carried out using "free lime content: 8 mass%" as the second threshold value. In the second judgment step, for both the invention examples 1 and 2, for the slag whose free lime content was determined to be equal to or greater than the second threshold value, it was decided in the decision step that the slag would not be steam aged and would be used for purposes other than roadbed material. For the slag whose free lime content was determined to be less than the second threshold value, it was decided in the decision step that the slag would be steam aged and used for roadbed material. An expansion test was carried out on the slag material after the steam aging treatment, and for the slag that failed the expansion test, the steam aging treatment was repeatedly carried out until the expansion test was passed. The conditions for one steam aging treatment in the examples are as follows. Slag loading volume: 1000t Aging time per cycle: 96 hours Steam temperature: 100℃ Steam inflow conditions: Steam is passed uniformly through the slag so that the slag temperature reaches 90°C or higher before 48 hours have elapsed.

[0039] On the other hand, in Comparative Examples 1 and 2, it was decided to subject all the slag to steam aging without carrying out the second judgment step and to use it as roadbed material. An expansion test was carried out on the slag material after the aging treatment, and for the slag that failed the expansion test, the steam aging treatment was repeated until it passed the expansion test. The results of Invention Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0040] [Table 1]

[0041] As shown in Table 1, in invention examples 1 and 2, slags were selected for free lime analysis based on the maximum free lime content, so the implementation ratio of free lime analysis was 43% (invention example 1) and 24% (invention example 2) of the total number of slags. This made it possible to reduce the number of free lime analyses of slags while avoiding an increase in the number of slags that fail the expansion test after one steam aging treatment, and confirmed that it was possible to suppress an increase in the cost of slag treatment.

[0042] In addition, in invention examples 1 and 2, the average number of times the steam aging treatment was performed was 1.02 times (invention example 1) and 1.00 times (invention example 2). In invention examples 1 and 2, for slag whose free lime content analyzed in the analysis step was 8% by mass or more, it was decided in the determination step that the slag would not be steam aged and would be used for an application other than roadbed material. As a result, the number of slags that failed the expansion test after one steam aging treatment was reduced, and it was confirmed that almost all of the slag that had been steam aged passed the expansion test after one steam aging treatment.

[0043] On the other hand, in Comparative Examples 1 and 2, the first judgment step was not performed, and therefore the analysis step was performed on all the slag. As a result, it was not possible to suppress the increase in the cost of processing the slag. In addition, since all the slag was subjected to the steam aging treatment, many slags failed the expansion test after one steam aging treatment. In fact, the average number of times the steam aging treatment was performed was 1.23 (Comparative Example 1) and 1.08 (Comparative Example 2), and the number of slags that failed the expansion test after one steam aging treatment and required multiple steam aging treatments increased.

[0044] These results confirmed that by deciding whether or not to steam age the slag based on the free lime content analyzed in the analysis process and the judgment results in the second judgment process, it is possible to increase the percentage of slag that passes the expansion test with one steam aging treatment. If the expansion test passes with one steam aging treatment, additional treatment will not be necessary, which will further reduce the increase in the cost of steam aging treatment.

Claims

1. An estimation step of estimating a maximum free lime content contained in slag generated in the refining from the component composition of auxiliary materials used in the refining of molten iron and the Si concentration of the molten iron before the refining; a first determination step of determining whether the maximum free lime content of the slag estimated in the estimation step is equal to or greater than a first predetermined threshold value; A determination step of determining a method for treating the slag based on the result determined in the first determination step; The method for managing slag comprising the steps of:

2. In the estimation step, T.CaO and T.SiO are calculated from the Si concentrations of the auxiliary materials and the molten iron before refining. ２ Calculate the T. CaO and T. SiO ２ 2. The method of claim 1, further comprising estimating the maximum free lime content using:

3. The slag management method according to claim 2 , wherein in the estimation step, the maximum free lime content of the slag is estimated using the following formula (1): Maximum free lime content = T. CaO-1.86 × T. SiO ２ ・・・(1)

4. an analysis step of analyzing the free lime content of the slag determined to be equal to or greater than the first threshold value in the first determination step; A second determination step of determining whether the free lime content analyzed in the analysis step is equal to or greater than a predetermined second threshold value; having A slag management method according to any one of claims 1 to 3, wherein in the determination step, a method for treating the slag is determined based on the results determined in the first judgment step and the second judgment step.

5. The slag management method according to any one of claims 1 to 3, wherein the first threshold value is 15 kg / t-molten iron.

6. The slag management method according to claim 4, wherein in the determination step, it is decided that slag whose free lime content is determined to be equal to or greater than the second threshold value in the second judgment step will not be subjected to steam aging treatment.

7. A method for producing a slag material, comprising treating the slag with a treatment method determined in a determination step of the slag management method according to any one of claims 1 to 3 to produce a slag material.

8. A method for producing a slag material, comprising treating the slag with a treatment method determined in a determining step of the slag management method according to claim 4 to produce the slag material.

9. A method for producing a slag material, comprising treating the slag with a treatment method determined in a determining step of the slag management method according to claim 5 to produce the slag material.

10. A method for producing a slag material, comprising treating the slag with a treatment method determined in a determining step of the slag management method according to claim 6 to produce the slag material.

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