JP2022175823A - Method for producing blast furnace annealing slag, method for producing coarse aggregate for concrete, method for producing roadbed material, and blast furnace annealing slag - Google Patents

Abstract

To reduce elution of selenium from slag after annealing by controlling annealing conditions of molten slag.SOLUTION: A method for producing blast furnace annealing slag has a deposition process in which molten blast furnace slag is discharged into a cooling yard 1 to form a slag deposit 2, and a sprinkling process in which water of 50 L or more per ton of slag is sprinkled on a surface of the slag deposit 2 formed in the deposition process.SELECTED DRAWING: Figure 3

Description

TECHNICAL FIELD The present invention relates to a method for producing air-cooled blast furnace slag, a method for producing coarse aggregate for concrete, a method for producing roadbed material, and air-cooled blast furnace slag.

Slag produced in a blast furnace is classified into vitreous granulated blast furnace slag and crystalline air-cooled blast furnace slag depending on the cooling conditions. Of these, slow-cooled blast furnace slag is poured into a cooling yard in a molten state and slowly cooled by natural cooling and moderate water sprinkling. After that, it is crushed and sieved, and aged if necessary, and then used as a roadbed material or a coarse aggregate for concrete.

In recent years, due to the depletion of high-grade raw materials used in blast furnace operations, we are forced to use low-quality raw materials. Depending on the components of the raw material, the selenium content in the slag produced during blast furnace operation increases, and therefore the amount of selenium eluted from the slow-cooled slag may also increase.

As mentioned above, as a subsequent use of the air-cooled blast furnace slag, it is required to be used as a roadbed material for roads and as a coarse aggregate for concrete. 0058-1 Chemical substance test method for slag” and “Environmental Agency Notification No. 46”.

Here, as a countermeasure against the elution of selenium from slow-cooled blast furnace slag, for example, Patent Document 1 discloses a method of suppressing the elution of selenium by contacting iron and steel slag with an acid gas in the presence of water. Further, Patent Document 2 discloses a method for removing selenium from slag by wet processing.

JP 2013-234111 A JP 2019-162610 A

However, the techniques disclosed in Patent Document 1 and Patent Document 2 are methods of treating the cooled, slowly cooled slag as a target, and there is a problem that the number of slag treatment steps increases.

The present invention has been made in view of such circumstances, and by controlling the slow cooling conditions of the molten slag, while suppressing an increase in the processing steps of the slag after slow cooling, selenium is released from the slag after slow cooling. The purpose is to reduce the amount of elution.

The gist and configuration of the present invention for solving the above problems are as follows.
[1] A deposition step of flowing molten blast furnace slag into a cooling yard to form slag deposits, and sprinkling 50 L or more of water per ton of slag on the surface of the slag deposits formed in the deposition step. and a method for producing air-cooled blast furnace slag.
[2] The method for producing air-cooled blast furnace slag according to [1], further comprising a drying step in which the surface of the slag deposit is left to dry after watering in the watering step is stopped.
[3] After the drying step, the deposition step and the watering step are further performed, and the drying step, the deposition step, and the watering step are regarded as one cycle, and the cycle is repeated one or more times to form a layered slag deposit. The method for producing slow-cooled blast furnace slag according to [2].
[4] A method for producing coarse aggregate for concrete, comprising crushing and sieving air-cooled blast furnace slag produced by the method for producing air-cooled blast furnace slag according to any one of [1] to [3].
[5] Roadbed material for roads manufactured by crushing and aging blast furnace slow-cooled slag produced by the method for producing slow-cooled blast furnace slag according to any one of [1] to [3]. manufacturing method.
[6] Air-cooled blast furnace slag having a void area of 4.5% or less.

By using the method for producing slow-cooled blast furnace slag according to the present invention, the slow-cooling conditions for the molten blast-furnace slag are optimized, the amount of selenium eluted from the slow-cooled slag is reduced, and the subsequent treatment steps of the slow-cooled slag. increase can be suppressed. As a result, it can be used as a roadbed material and a coarse aggregate for concrete. In addition, there is also the effect that a high-quality aggregate with a low water absorption can be obtained.

4 is a graph showing the relationship between the void area of slag and the selenium elution amount. FIG. 4 is a schematic diagram showing the state of voids generated inside the slag. FIG. 4 is a schematic diagram showing a slow cooling method for slag deposits in a cooling yard. 4 is a graph showing the relationship between air cooling time and void area. It is a figure which shows an example of the comparison result of an invention example and a comparative example using image analysis.

The present inventors have completed the present invention based on the finding that the slow cooling conditions for molten blast furnace slag affect the elution of selenium from the slow cooled blast furnace slag. Hereinafter, the present invention will be described through embodiments of the invention.

FIG. 1 is a graph showing the relationship between the void area of slag and the selenium elution amount. The horizontal axis of FIG. 1 is the slag void area (%). The slag void area (%) refers to the area existing within a given slag cross-sectional area (void area/slag area×100). A specific example of the void area on the image will be described later in Examples. The vertical axis in FIG. 1 represents the elution amount (mg/L) of selenium, which is the elution amount measured according to the method of Notification No. 46 of the Environment Agency. As shown in FIG. 1, the smaller the void area of the slag, the smaller the amount of selenium eluted from the slag.

Voids within the slag are formed by the generation of sulfur-based gas. Since the apparent viscosity of the slag is high when the slag is in a state of a mixture of a liquid phase and a solid phase, it is difficult for the gas generated inside to escape to the outside, and after slow cooling, the slag exists as voids. Therefore, in order to reduce the voids in the slag, the temperature range in which the mixed state of the liquid and solid phases is maintained must be cooled rapidly. It is effective to reduce the amount of gas generated. In blast furnace slag, the temperature range in which the mixed state of the liquid phase and the solid phase is maintained is about 1200°C to 1350°C.

Next, the state of selenium elution in slowly cooled blast furnace slag will be described with reference to FIG. FIG. 2 is a schematic diagram showing the state of voids generated inside the slag. FIG. 2(a) shows a state in which the voids (recesses in the drawing) are small (small) inside the slag, and FIG. 2(b) shows a state in which the voids are large (many). As shown in FIG. 2, the contact area between the slag surface and the surrounding water is smaller when the gaps are smaller (smaller) and larger when the gaps are larger (more).

Since selenium is eluted to the outside of the slag through the surrounding water, the smaller the contact area with water, the smaller the amount of selenium that is eluted to the outside through water. Furthermore, by reducing the voids inside the slag, a high-quality slow-cooled slag with a low water absorption rate can be obtained. If the pores are small (small), the influence of selenium enrichment on the surface of the pores is small, so the elution of selenium is suppressed.

Next, the slow cooling method for slag according to the present embodiment will be described with reference to FIG. 3(a)-(b) show a conventional slag slow-cooling method, and FIGS. 3(c)-(e) show a slag slow-cooling method according to the present invention, respectively, as simplified schematic diagrams.

First, in the conventional slag slow cooling method, as shown in FIGS. The slag deposit 2 is deposited by pouring (see FIG. 3(a)), and then, as shown in FIG. ) from above the uppermost layer, cooling water 4 discharged from a water supply device 3 such as a water gun is allowed to slowly cool all the slag deposits at once.

On the other hand, in the slag slow cooling method according to the present embodiment, as shown in FIG. 50 L or more of cooling water 4 is sprinkled.

In the slag deposition step, the molten slag may be flowed in multiple steps. When transporting slag from the blast furnace to the cooling yard 1, tens to hundreds of tons of slag discharged in one tapping of the blast furnace is divided and transported to a plurality of slag pots. Since the slag pots are successively flowed to the cooling yard 1, the outflow of slag is interrupted while the slag pots are replaced, resulting in a period of air cooling. The deposition process includes this air-cooled period. Furthermore, the accumulation process may be a period of accumulating slag discharged from a plurality of times of tapping, not limited to one time of tapping in the blast furnace.

The deposition process is continued until the surface of the slag deposit 2 from which the last slag has flowed has solidified. Immediately after the molten slag was poured into the cooling yard 1, that is, while the surface of the slag deposit 2 was still flowing, the surface of the slag layer was not solidified. This is not preferable because water enters the molten slag layer and creates a danger of steam explosion. The time until the surface of the slag deposit 2 hardens and watering can be started depends on the temperature of the slag flowing into the cooling yard 1, but normally watering can be started about 15 minutes after the watering is finished.

For this reason, in this embodiment, after the slag is discharged into the cooling yard 1, it is air-cooled for at least 15 minutes or more to solidify the surface of the slag deposits 2, and then watering is started. If the slag is air-cooled for more than 48 hours, the solidification of the inside of the slag progresses, and the effect of controlling the slow cooling speed in the temperature range of 1200°C to 1350°C is reduced. A preferred time for air cooling is 30 minutes to 24 hours.

FIG. 4 is a graph showing the relationship between air cooling time and void area. In this embodiment, the lower limit of the air cooling time is set to 15 minutes or more, and this is because, as described above, if the air cooling time is less than 15 minutes, water is sprinkled from the surface of the slag layer to the inside, and a steam explosion may occur. . Further, in the present embodiment, the upper limit of the air cooling time is 48 hours or less, and as shown in FIG. 4, air cooling over 48 hours increases the void area in the slag (the slope in the graph increases). , a large amount of selenium may be eluted.

The reason why the amount of water sprayed is set to 50 L or more per ton of slag is that if the amount is less than 50 L, a sufficient effect of reducing the elution of selenium cannot be obtained. Although the watering time is not particularly limited, it is preferably 1 hour or longer, more preferably 3 hours or longer.

Regarding the temperature during slow cooling of the slag, it is important to spray as much water as possible within a temperature range of approximately 1200°C to 1350°C. Therefore, it is preferable to spray 50 L or more of water per ton of slag in this temperature range. However, while the temperature of the slag surface in contact with water is likely to drop, the temperature inside the slag is difficult to drop.

Furthermore, in the present embodiment, the surface of the slag deposit can be dried by the internal heat (drying process) by leaving it for a predetermined time after watering the surface of the slag is stopped.

In this embodiment, molten blast furnace slag is poured into a cooling yard and air-cooled for 15 minutes or more to solidify the surface of the slag layer. At this time, the inside of the slag layer is in a state of only a liquid phase, or a state in which both a liquid phase and a solid phase exist. By sprinkling 50 L or more of water per ton of slag in this state, elution of selenium from the slag after slow cooling can be reduced.

Furthermore, in this embodiment, as shown in FIGS. may be dried. Alternatively, the slag deposit 2 may be formed by pouring molten slag onto the slag deposit 2 whose surface is dry to form a new slag deposit on top of the slag deposit.

Specifically, the "deposition process" of the slag deposits by flowing molten blast furnace slag into the cooling yard, and the "drying process" of drying the surface of the slag deposits through the "watering process" of spraying water on the slag deposits. Then, the slag deposit whose surface has dried is further subjected to a "deposition process" and a "watering process", and the three processes of the "drying process", the "deposition process", and the "watering process" are combined into one. By repeating this cycle one or more times to stack layered slag deposits, the slag deposits formed each time are rapidly cooled in a temperature range in which the liquid phase and the solid phase are mixed. Not only can the cooling yard be operated efficiently.

In addition, since the slag deposit after slow cooling needs to be moved from the cooling yard by a shovel or the like, a large number of yards will be required if each layer is moved by a shovel or the like. On the other hand, in the present invention, it becomes possible to operate efficiently with a small number of cooling yards.

In order to efficiently operate the present invention in a cooling yard where the site area is limited, it is preferable that the thickness of the slag deposit is 0.3 to 3 m. If it is less than 0.3m, the frequency of movement with a shovel or the like will increase as described above. I don't like it.

The air-cooling time in this embodiment means the time from when the molten blast-furnace slag first started to flow into the cooling yard in the deposition process to when water was sprayed. For example, if the first flow of molten slag is started at 6:00 on a given day, the second flow is started at 12:00, and watering is started at 15:00, the cooling time will be 9 hours. When the cycle of "drying process", "accumulation process" and "sprinkling process" is repeated, it means the time from the time when blast furnace slag starts to flow out to the time when watering starts in each cycle.

By crushing and sieving blast furnace slag subjected to the method for producing slowly cooled slag according to the present embodiment, blast furnace slag Coarse aggregate (coarse aggregate for concrete) can be produced. Specifically, the water absorption rate of blast furnace slag coarse aggregate is defined as 6.0% or less for division L and 4.0% or less for division N, and the air-cooled slag produced by the method according to the present invention is , it becomes a good aggregate with few voids, that is, with a low water absorption rate.

Then, the slowly cooled blast furnace slag is crushed by the method according to the present embodiment, and if necessary, the particle size is adjusted by sieving or the like, and then the aging treatment is performed to obtain the road use related to "JIS 5015 road steel slag". Subbase material can be manufactured.

As described above, in the method for producing air-cooled blast furnace slag according to the present invention, molten blast furnace slag is allowed to flow into the cooling yard to form slag deposits, and after air cooling for 15 minutes or more or 48 hours or less, By sprinkling 50 L or more of water per ton of slag, it is possible to reduce the elution amount of selenium and produce dense slag with low water absorption.

Examples of producing slag using the method for producing slag according to the present embodiment will be described below.

In this example, air-cooled blast furnace slag was produced by changing the number of cycles, the thickness of slag deposits, the air-cooling time, and the amount of water sprinkled during the production of air-cooled slag. As described above, one cycle consisted of the three processes of "drying process", "depositing process" and "watering process" for the molten slag, and this cycle was repeated a predetermined number of times. As for the values of the air cooling time and the amount of water sprayed, the average value was adopted when two or more cycles were performed.

After slow cooling, the slag was removed from the cooling yard by a shovel, crushed and used as a sample. For the samples, the selenium elution amount was measured based on the selenium elution test according to the method of Notification No. 46 of the Environment Agency. In addition, resin filling and polishing were performed, and the void area was obtained by image analysis in microscopic observation. Furthermore, the crushed slag was sieved by 20 to 5 mm, and the water absorption was measured according to "JIS A 1110 Coarse Aggregate Density and Water Absorption Test Method".

Image analysis was performed by the following methods 1 to 4.
1. The crushed particles with a particle size of 5 to 15 mm are embedded in resin.
2. Polished to allow microscopic observation.
3. Take a picture at about 100 times (approximately 0.075 x 0.1 mm).
4. The void area was calculated using image analysis software.
Regarding the calculation of the void area, the void areas of five slag particles were calculated for each cooling condition, and the average value of the three slag particles, excluding the maximum and minimum values, was expressed as the void area.
In this example, the void area was calculated as the ratio (%) of the total area of voids to the area of the photograph taken by the above method. Table 1 shows the production conditions, void area, amount of selenium elution, and water absorption of coarse aggregate for the air-cooled blast furnace slag.

The image shown in FIG. 5(a) shows the image analysis result of Invention Example 6 in Table 1, and the slow cooling conditions in Invention Example 6 are air cooling time of 0.25 h and water spraying amount of 200 L / t-slag. It's becoming As a result, the void area was 0.5% and the selenium elution amount was 0.003 mg/L.

The image shown in FIG. 5(b) shows the image analysis results of Comparative Example 4 in Table 1, and the slow cooling conditions in Comparative Example 4 are an air cooling time of 0.25 h and a water spray amount of 10 L / t-slag. It has become. As a result, the void area was 7.9% and the selenium elution amount was 0.017 mg/L.

In other words, due to the difference in the slow cooling conditions of the blast furnace slag, especially the amount of water sprayed, there was a large difference in the area of the voids (the black voids in the drawing), and as a result, it was confirmed that there was also a difference in the selenium elution amount. did it.

Next, examples according to Invention Examples-1 to Invention Examples-15 and Comparative Examples-1 to Comparative Examples-6 shown in Table 1 will be described.
In invention example-1 to invention example-3, the number of cycles was 1, the thickness of the slag deposit was 1 m, the amount of water sprayed was 200 L/t-slag, and the air cooling time was changed in the range of 3 to 48 hours. The amount of selenium eluted was 0.004 mg/L to 0.007 mg/L, all of which satisfied the soil environment standard value of 0.01 mg/L or less. However, the shorter the air-cooling time, the lower the selenium elution amount. From this result, it was confirmed that the shorter the air cooling time, the better.

In invention examples-1, invention examples-4, and invention examples-5, the amount of water sprinkled was changed in the range of 50 L/t-slag to 200 L/t-slag. The selenium elution amount was 0.01 mg/L or less. In addition, there was a tendency that the larger the amount of water sprinkled, the lower the amount of elution. From this result, it was confirmed that the larger the amount of water sprayed, the better.

In invention examples-6 to invention examples-8, the thickness of the slag deposit, the air cooling time, and the water sprinkling amount were changed. The selenium elution amount was 0.01 mg/L or less in each case.

In invention examples-9 to invention examples-15, the number of cycles was changed from 2 to 7, and other conditions were changed. The selenium elution amount was 0.01 mg/L or less in each case.

On the other hand, in Comparative Examples-1 to 3, the air cooling time exceeded 48 hours, and the selenium elution amount exceeded 0.01 mg/L. In Comparative Examples-4 to 6, the water spray amount is less than 50 L/t-slag, and the selenium elution amount exceeds 0.01 mg/L. In addition, the water absorption rate of the coarse aggregate was also higher than that of the present invention example.

From the above, the molten blast furnace slag of this example is poured into the cooling yard, air-cooled for 15 minutes or more and 48 hours or less, and then sprinkled with 50 L or more of water per ton of slag. It was confirmed that the air-cooled blast furnace slag with a /L or less can be produced.

In addition, the water absorption rate of the coarse aggregate of each invention example is 3.9% or less, and it is a high-quality coarse aggregate that satisfies the category N of "JIS A 5011-1 Slag aggregate for concrete Part 1: blast furnace slag aggregate". An aggregate was obtained. Furthermore, the slag that has been aged in the atmosphere for 3 months after crushing and grain size adjustment meets all the standards of grain size adjusted steel slag MS-25 and Crusheran steel slag CS-40 described in "JIS 5015 Steel slag for roads". Satisfied.

Furthermore, the produced slag has a selenium elution amount of 0.01 mg/L or less if the void area is 4.5% or less, and a selenium elution amount of slag with a void area of 4.5% or less is 0.01 mg/L. It was confirmed that the slag can be suppressed to L or less.

REFERENCE SIGNS LIST 1 cooling yard 2 slag deposits 3 water supply device 4 cooling water

Claims (6)

a deposition step for flowing molten blast furnace slag into a cooling yard to form a slag deposit;
a sprinkling step of sprinkling 50 L or more of water per ton of slag on the surface of the slag deposit formed in the depositing step;
A method for producing slow-cooled blast furnace slag. 2. The method for producing air-cooled blast furnace slag according to claim 1, further comprising a drying step of leaving the deposited slag until the surface of the slag deposit is dried after stopping watering in the watering step. The drying step is followed by the deposition step and the watering step, and the drying step, the deposition step, and the watering step are set as one cycle, and the cycle is repeated one or more times to form a layered slag deposit. 2. The method for producing slow-cooled blast furnace slag according to 2. A method for producing coarse aggregate for concrete, comprising crushing and sieving air-cooled blast furnace slag produced by the method for producing air-cooled blast furnace slag according to any one of claims 1 to 3. A method for producing a roadbed material by crushing and aging the blast furnace annealed slag produced by the method for producing blast furnace annealed slag according to any one of claims 1 to 3. Slow-cooled blast furnace slag having a void area of 4.5% or less.

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