JP5341849B2 - Manufacturing method of recycled slag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce recycled slag which is suppressed in elution of fluorine and used particularly for a roadbed material by mixing both of molten slag excellent in iron making treatment and ladle refining slag excellent in molten steel treatment. <P>SOLUTION: The recycled slag is produced by charging molten slag S1 having a low basicity to a removed slag vessel 1 to coat the removed slag vessel 1 with the molten slag S1, then charging ladle refining slag S2 produced in ladle refining into the removed slag vessel 1 coated with the molten slag S1 in a molten state and mixing the ladle refining slag S2 with the molten slag S1 so that the resulting mixed slag has a chemical composition comprising 34-52 mass% of CaO, 16-25 mass% of Al<SB POS="POST">2</SB>O<SB POS="POST">3</SB>, 18-26 mass% of SiO<SB POS="POST">2</SB>, 6-10 mass% of MgO, and the balance being inevitable impurities, and further cooling and subjecting the resulting slag to a hydration treatment. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a method for producing recycled slag.

  Conventionally, steelmaking slag such as blast furnace slag and converter slag is generated when molten iron is melted in a blast furnace or primary refining is performed in a converter. Such steelmaking slag is generally reused as converter slag or reused as roadbed material. However, when slag to be reused, that is, recycled slag is used as it is as a material for roadbed materials, elution of fluorine, which is a problem for the environment, may occur.

Therefore, when using the slag after a process as a material of a roadbed material, it is necessary to suppress the elution of fluorine by modifying the slag after the process. As techniques for suppressing elution of fluorine, for example, there are those shown in Patent Documents 1 to 7.
In Patent Document 1, converter slag and blast furnace slag or desiliconized slag are discharged into the same pit or yard, and immediately thereafter, the molten or semi-molten slag is cultivated to convert the converter slag and blast furnace slag or desiliconized slag. Slag is reformed by mixing with soot.

In Patent Document 2, a substance having a relatively high basicity is allowed to act on the blast furnace slag in a molten state outside the blast furnace, so that an acidic component in the blast furnace slag and a basic component in a substance having a relatively high basicity are used. Are made to react with each other using sensible heat of the blast furnace slag so that recycled slag can be obtained from the blast furnace slag.
In Patent Document 3, a fluorine-containing steelmaking slag and coal ash are simultaneously added to and melted in a molten blast furnace slag, and then cooled and solidified to obtain a blast furnace slag having a fluorine concentration of 2.5 mass% or less. I have to.

In patent document 4, 90-10 mass% of steelmaking slag is contained with respect to 10-90 mass% of blast furnace slow cooling slag.
In Patent Document 5, one or more mixing ratios selected from blast furnace granulated slag and fly ash with respect to the steelmaking slag are 1 to 50% by weight of the steelmaking slag amount.
In Patent Document 6, the steelmaking slag including serving workpiece _{fluorine, CaO · Al 2 O 3,} 5CaO · 3Al 2 O 3, 12CaO · 7Al 2 O 3, 9CaO · 5Al 2 O 3, 2CaO · Al 2 O 3 3CaO · Al ₂ O ₃ , or a mixture thereof, or a powder containing these hydrates, and one or a combination of two or more of blast furnace slow-cooled slag, blast furnace granulated slag, concrete scrap and coal ash By adding both, elution of the fluorine is suppressed.

In Patent Document 7, at least one of CaO, Al ₂ O ₃ , metal Al, and Al—is added to the converter slag or the electric furnace slag, which is an agent to be treated that is generated when the molten steel is processed in the smelting furnace. by adding, in mass%, CaO: 45~60%, Al 2 O 3: 30~55%, SiO 2: 10% or less, and T. Fe: with containing 3% or _{less, 3CaO · Al 2 O 3,} 12CaO · 7Al 2 O 3, CaO · Al 2 O 3, 5CaO · 3Al 2 O 3, 9CaO · 5Al 2 O 3, 2CaO · Al 2 O A stabilizer for steelmaking slag containing fluorine, which contains at least one of the _three as a mineral phase, is manufactured.

Japanese Patent Laid-Open No. 06-329451 Japanese Patent Laid-Open No. 10-279331 Japanese Patent Laid-Open No. 2007-22818 Japanese Patent No. 4264523 JP 2001-72447 A Japanese Patent No. 3606108 Japanese Patent No. 3606107

In Patent Documents 1 to 3 described above, for example, two slags such as blast furnace slag and converter slag are mixed, thereby generating mixed slag in which elution of fluorine is suppressed, and this mixed slag is recycled slag. It can be used as
However, Patent Documents 1 to 3 only show the idea of reforming slag by mixing two slags. The chemical component range (composition range) of the first slag and the second The chemical composition range of the slag is not disclosed in detail. Therefore, even if the techniques of Patent Documents 1 to 3 are used, the actual situation is that the slag cannot be reliably reformed.

Moreover, although the chemical component of the mixed slag is disclosed in Patent Document 4, it is not disclosed what kind of slag is mixed and reforming the slag, and the technique of the Patent Document 4 is used. However, as in Patent Documents 1 to 3, the actual situation is that slag cannot be reliably reformed.
Although Patent Documents 5 to 7 describe the composition of blast furnace slag and refining slag, and mixing two slags, it is still necessary to reliably reform slag even using these techniques. The fact is that you can't.

  Therefore, in view of the above problems, the present invention, when producing recycled slag, particularly by mixing two slags of hot metal slag and ladle smelting slag, which are defined to be excellent in the steelmaking process and the steelmaking process, It aims at providing the manufacturing method of the recycling slag which enables manufacture of the recycling slag with few elution of fluorine used for roadbed materials.

In order to achieve the above object, the present invention has taken the following measures.
That is, the technical means for solving the problem in the present invention is that, when producing recycled slag, the chemical components are CaO: 24 to 50% by mass, Al ₂ O ₃ : 1 to 16% by mass, SiO ₂ : 17 to 38% by mass, MgO: 0.3 to 10% by mass, the remainder being inevitable impurities and CaO / SiO ₂ : 1 to ₂ was added to the waste container, and the waste metal slag was used to remove the waste The inner surface of the container is coded, and the chemical components are CaO: 33 to 66% by mass, Al ₂ O ₃ : 22 to 48% by mass, SiO ₂ : 3 to 16% by mass, MgO: 5 to 11% by mass and the balance There unavoidable impurities and is and CaO / SiO _2: a ladle refining slag becomes 3 or more, the charged in the molten state in Haikasu container coated by hot metal slag, the chemical components of the mixture were mixed slag, CaO: 4-52 wt%, Al ₂ O _3: 16~25 wt%, SiO _2: 18 to 26 wt%, MgO: a 6-10% by weight as the balance being inevitable impurities, cooling the mixture slag The point is that hydration is performed later.

  According to the present invention, when manufacturing recycled slag, it is used especially for roadbed materials by mixing two slags of hot metal slag and ladle refining slag which are specified to be excellent in the steelmaking process and steelmaking process. Recycled slag with less fluorine elution can be produced.

It is the schematic which showed the procedure of the modification | reformation of slag. It is a ternary phase diagram of CaO, SiO ₂ , Al ₂ O ₃ showing a liquid phase region at 1500 ° C. when MgO is 5 mass% and 10 mass% in a ladle refining slag. It is a related figure of the quantity of MgO of a ladle refining slag, and a liquid phase rate. It is a relationship figure of a slag mixing rate and the elution amount (F elution amount) of fluorine. CaO for each slag composition is a state diagram in terms of ternary SiO _2, Al ₂ O _3. (A) SEM image of the mixed slag remaining after the F dissolution test, (b) An image obtained by extracting a region where fluorine exists by performing a mapping process with EPMA on the SEM image. (A) Relationship diagram between Al ₂ O ₃ concentration in slag and Al elution amount, (b) Relationship diagram between Al ₂ O ₃ concentration in slag and Al elution rate. (A) Relationship diagram between Al ₂ O ₃ concentration in slag and Ca elution amount, (b) Relationship diagram between Al ₂ O ₃ concentration in slag and Ca elution rate. (A) Relationship diagram between Al ₂ O ₃ concentration in slag and F elution amount, (b) Relationship diagram between Al ₂ O ₃ concentration in slag and F elution rate. It is a graph showing the relationship between the concentration of Al ₂ O ₃ and F dissolution rate of each slug in the slag. It is a related figure of a hydration process and F elution amount.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
When fluorine is contained in slag produced by various processes of steelmaking, there is a concern about fluorine elution when the slag is reused as a roadbed material. For this reason, in the conventional technology, for example, a refining method that does not use CaF ₂ (fluorite) that has been used for lowering the melting point in secondary refining is considered, and slag after treatment is devised by devising refining treatment. In order not to contain fluorine.

However, even if processing is performed in consideration of secondary refining that does not use CaF ₂ , the raw materials (for example, lime), refractories, and iron alloys that are the source of slag inevitably contain trace amounts of fluorine. The later slag always contained fluorine.
Therefore, the present invention has found a method for improving the slag after treatment, that is, a method for producing recycled slag so as not to elute as much as possible the fluorine that is inevitably contained in the slag by the fluorine derived from the raw material.

Specifically, by mixing the two treated slags, a slag with very little fluorine elution was generated, and the two treated slags could be used as recycled slag.
As shown in FIG. 1, first, the molten iron slag S1 generated when the molten iron is produced in the blast furnace is discharged into the waste container 1, and the inner surface (inner wall side) of the waste container 1 is discharged by the molten metal slag S1. The surface). Thereafter, ladle slag S1 and ladle slag S2 are mixed by charging ladle smelting slag S2 in a molten state into the waste container 1 whose inner surface is coated, and this mixed slag is hydrated. By doing so, recycled slag S3 in which elution of fluorine is suppressed is manufactured.

Hereinafter, the manufacturing method of a recycling slag is demonstrated in detail.
[About hot metal slag]
In mixing the two slags, the first slag is the hot metal slag S1 having a CaO / SiO ₂ (basicity) of 1-2 and a low basicity. This hot metal slag S1 is, for example, a blast furnace slag that is generated when hot metal is made.

Specifically, the chemical component (composition) of the hot metal slag S1 is CaO: 24 to 50% by mass, Al ₂ O ₃ : 1 to 16% by mass, SiO ₂ : 17 to 38% by mass, MgO: 0.3 to 10% by mass. %, The balance being inevitable impurities.
The hot metal slag S1 will be described by taking a blast furnace slag as an example.
CaO is introduced into a blast furnace in order to remove sulfur contained in coke and impurities contained in iron ore.

Al ₂ O ₃ is contained in iron ore that is a raw material for hot metal. In the blast furnace, iron ore undergoes a reduction reaction of Fe _t O by reaction with carbon (CO gas), and other components contained in the iron ore are partly reduced and contained in the hot metal, Al ₂ O ₃ hardly dissolves in the blast furnace, so it dissolves in the blast furnace slag.
SiO ₂ is contained in iron ore like Al ₂ O ₃ . Although SiO _{2 is} also included in the hot metal when the iron ore is reduced, it is dissolved in the blast furnace slag in the same manner as Al ₂ O ₃ .

MgO is contained in iron ore and refractories in the blast furnace, and in the blast furnace, it is dissolved in the blast furnace slag without being reduced.
The balance is unavoidable impurities such as FeO, MnO, CaS, P ₂ O ₅ , TiO ₂ , and Na ₂ O.
The CaO / SiO ₂ (basicity) of the hot metal slag S1 is adjusted by quick lime introduced into the blast furnace when making hot metal in the blast furnace.

As long as the hot metal slag S1 satisfies the above-described composition range, not only the blast furnace slag but also the blast furnace desiliconized slag generated when the hot metal is desiliconized in the blast furnace casting floor. The hot metal pretreatment slag generated when the hot metal is processed with a ladle or a kneading car before the secondary refining may be used.
[About ladle refining slag]
The second slag is ladle refining slag S2 generated when ladle refining is performed.
This ladle refining slag S2 is mainly composed of CaO, and is used to deoxidize molten steel with Si or Al during ladle refining. CaO—Al ₂ O ₃ -SiO ₂ -MgO-based slag. The ladle refining slag S2 is used, for example, during secondary refining in order to melt low oxygen and / or low sulfur steel.

Specifically, the chemical composition of ladle refining slag S2 (composition) is CaO: 33-66 wt%, Al ₂ O _3: 22~48 wt%, SiO _2: 3 to 16 wt%, MgO: 5 to 11 mass %, The balance being inevitable impurities. The ladle refining slag S2 will be described.
When molten steel is discharged from a converter or electric furnace, slag (containing SiO ₂ ) in the converter or electric furnace, slag adhering to the ladle, remaining steel remaining in the ladle (oxidized Fe _t O) Etc., the molten steel is oxidized, and the oxygen concentration in the molten steel tends to increase.

Therefore, the secondary in order refining, using a ladle refining slag S2 and the Al containing _{CaO, 3SiO 2 + 4Al = 3Si} + 2Al 2 O 3, 3Fe t O + 2Al = 3tFe + Al 2 by the reaction as shown in O ₃ of the molten steel and slag By performing deoxidation, the treatment of lowering O _t (the oxygen level in the steel) in the molten steel is performed to melt the low oxygen steel.
Thus, in order to melt low oxygen steel, the target value of the oxygen level in the steel is generally 9 ppm as disclosed in Japanese Patent No. 3018355 and Japanese Patent Application Laid-Open No. 2006-200027. . And in order to make the oxygen level in steel 9 ppm or less, it is desirable that the basicity of the ladle smelting slag S2 is high basicity. Specifically, the basicity needs to be 3 or more. In addition, the basicity needs to be 3 or more in order to melt low-sulfur steel.

Further, quicklime ladle refining slag S2 (CaO) is highly reactive with Al ₂ O _3, since the adsorbing Al ₂ O ₃ (inclusions) generated in the molten steel during deoxidation by Al, CaO The amount of is preferably larger than that of SiO ₂ . That is, when performing ladle refining, it is desirable to make CaO rich with a relatively large amount of CaO, and CaO is preferably 33 to 66% by mass.

As described above, in the ladle refining slag S2, it is desirable that the amount of SiO ₂ is smaller than that of CaO, but when the primary refining such as the converter is finished and the molten steel is produced, the processing of the converter is performed. The converter slag generated in step inevitably enters, and the amount of SiO _{2 in} the ladle refining slag S2 is at least 3% by mass. In addition, in order to stably make the basicity 3 or more, it is desirable to make SiO ₂ 16 mass% or less.

Al ₂ O ₃ has the effect of lowering the melting point like SiO ₂ and is necessary so that CaO can be melted at about 1500 ° C., but the amount of Al ₂ O ₃ in the ladle refining slag S2 is large. When Al ₂ O ₃ approaches saturation, the activity of Al ₂ O ₃ increases, and the adhesion removal property between the Al ₂ O ₃ inclusions in the molten steel and the ladle refining slag S2 (for example, adsorbs) Time will be very long). That is, since the too large deoxidation effect is Al ₂ O ₃ concentration in the ladle refining slag S2 is suppressed, when viewed from the actual operation, Al ₂ O ₃ in the ladle refining slag S2 are more than 48 wt% It is necessary to.

FIG. 2 shows a ternary system of CaO, SiO ₂ and Al ₂ O ₃ showing a liquid phase region at 1500 ° C. when MgO is 5 mass% and 10 mass% in the ladle refining slag S2 It is a state diagram.
As shown in FIG. 2, when the ranges of CaO, SiO ₂ and Al ₂ O ₃ described above are summarized, when MgO is 5% by mass, CaO, SiO ₂ and Al ₂ O ₃ of ladle refining slag S2 are When the range is A and MgO is 10% by mass, the CaO, SiO ₂ , and Al ₂ O ₃ of the ladle refining slag S2 are the range B.

Moreover, when performing ladle refining, since the refractory of the ladle is based on MgO, MgO is added in order to prevent the refractory from being melted as much as possible. When MgO (% MgO) in the ladle refining slag S2 is 5% by mass or more, the refractory can be prevented from melting.
However, as shown in FIG. 3, when the amount of MgO added is too large and MgO (% MgO) in the pot refining slag becomes larger than 11% by mass, it solidifies and the fluidity of the slag deteriorates. The liquid phase ratio may be less than 100%. Therefore, MgO in the ladle refining slag S2 needs to be 11 mass% or less.

  In addition, the liquid phase rate of slag shows the ratio of the liquid phase in slag, and can be calculated | required with thermodynamic equilibrium calculation software (FactSage Ver.6.0) based on the chemical component in slag. In general, the closer the slag liquid phase rate is to 0%, the worse the slag meltability is. The closer the slag liquid phase rate is to 100%, the better the slag meltability. When the liquid phase ratio is 100%, it is considered that the fluidity (reactivity) of the slag is high. For example, when the liquid phase rate of slag is 100%, the molten steel can be continuously covered with the ladle refining slag S2, and when the ladle refining slag S2 is discharged, the ladle refining slag S2 is placed in the ladle. There is also an advantage that it is difficult to remain.

The balance is unavoidable impurities, such as Fe _t O, MnO, Na ₂ O, and the like. When molten steel is discharged from the converter, converter slag is inevitably mixed in, or elution occurs from the refractory in the ladle during refining of the ladle, or some compounds are reoxidized. Therefore, the ladle smelting slag S2 inevitably contains a trace amount of inevitable impurities as described above.
[About mixed slag]
In the present invention, by mixing the molten iron slag S1 and the ladle refining slag S2, new slag (mixed slag) that can suppress fluorine elution is generated.

  More specifically, first, the molten iron slag S1 is charged into the waste container 1 that does not contain slag, in other words, the waste container 1 after the slag is discharged. When the molten iron slag S1 in the waste container 1 is in a molten state (before all the molten iron slag S1 is solidified), for example, the molten metal slag S1 in the waste container 1 is tilted by tilting the waste container 1. As a result, hot metal slag S1 is attached to the entire inner wall of the waste container 1, and the inner wall is coded by the hot metal slag S1.

In addition, since what is necessary is just to code the inner wall of the waste container 1 by hot metal slag S1, any method may be sufficient as the coding method. For example, after the molten metal slag S1 is charged into a full cup of the waste container 1, the molten metal slag S1 is tilted to discharge the molten metal slag S1, thereby coding the molten metal slag S1 up to the upper end of the inner wall of the waste container 1. May be.
Next, the ladle refining slag S2 is charged into the waste container 1 whose inner wall is coded by the molten iron slag S1. The ladle refining slag S2 is in a molten state during the ladle refining, but after being discharged from the ladle, it is gradually cooled and begins to solidify. When the ladle refining slag S2 is completely solidified, it becomes difficult to react with the molten iron slag S1, so for example, when the ladle refining slag S2 is 1400 ° C. or higher and is in a molten state, the ladle refining slag S2 is put into the waste container 1 and mixed with the molten iron slag S1. The temperature of the molten steel after ladle refining is about 1500 ° C.

  FIG. 4 shows the relationship between the slag mixing ratio and the fluorine elution amount (F elution amount). In FIG. 4, a slag mixing rate of 0% indicates that the ladle smelting slag S2 is 100%, and a slag mixing rate of 100% indicates that the hot metal slag S1 is 100%. Yes. That is, the slag mixing ratio of 0% and 100% indicates a case where the molten iron slag S1 and the ladle refining slag S2 are not mixed at all.

As shown in FIG. 4, when considering the situation where hot metal slag S1 and ladle refining slag S2 are mixed, as in the present invention, when hot metal slag S1 and ladle refining slag S2 are melted and mixed at a high temperature, The amount of F elution tends to be suppressed as compared with the case where the molten iron slag S1 and the ladle refining slag S2 are mixed with each other (physical mixing).
For example, rather than mixing both hot metal slag S1 and ladle refining slag S2 in powder (granular form) and mixing (physical mixing), it is better to melt and mix hot metal slag S1 and ladle refining slag S2 at a high temperature. The amount of elution can be suppressed. The melt mixing (mixing in a molten state) may be in a molten state when at least one of the molten iron slag S1 or the ladle refining slag S2 is mixed. When mixing, it is better that the ladle refining slag S2 having a high melting point is in a molten state.

  The method for putting the ladle refining slag S2 into the waste container 1 is not particularly limited. For example, when the ladle refining slag S2 in the ladle is discharged to the outside, the ladle refining slag S2 in the ladle may be directly put into the waste container 1, or once the ladle in the ladle The refining slag S2 may be put into another container, and then the ladle refining slag S2 in another container may be put into the coated waste container 1. When the ladle refining slag S2 in the ladle is directly put into the waste container 1, in order to prevent the temperature of the ladle refining slag S2 from dropping, the molten steel is left in the ladle as a heat source, and the ladle refining slag S2 It is preferable to ensure the fluidity of.

Chemical components in the mixed slag (composition) is, CaO: 34-52 wt%, Al ₂ O _3: 16~25 wt%, SiO _2: 18 to 26 wt%, MgO: the balance a 6-10 wt% Inevitable impurities.
Thus, when the chemical component of the mixed slag is in the range as described above, gehlenite is generated in the mixed slag. That is, as shown in FIG. 5, when the molten iron slag S1 and the ladle refining slag S2 are mixed in a molten state of 1400 ° C. or higher and the mixed slag is in the above range, mixed slag having gehlenite can be generated. it can.

Gerenite is a mineral (C ₂ AS) in a molar ratio of CaO: Al ₂ O ₃ : SiO ₂ = 2: 1: 1, and after hydration, C ₂ AS · 8H ₂ O (Stratlingite) Become. Gelenite has low water solubility and has a role of immobilizing fluorine so that it does not elute after hydration.
FIG. 6 is a summary of what was left over when the fluorine elution test was performed on the mixed slag. Specifically, FIG. 6A is an image of the residual mixed slag by SEM (Scanning Electron Microscope), and FIG. 6B shows an image obtained by mapping fluorine with EPMA.

  As shown in FIGS. 6A and 6B, when the mixed slag is viewed, there is a portion where fluorine is concentrated as shown by an arrow A. When the composition ratio of the portion where the fluorine is concentrated is analyzed by EPMA (Electron Probe MicroAnalyser), it is as shown in Table 1.

As shown in Table 1, the crystal structure of the portion where fluorine is concentrated is strutlingite which is a hydrate of gehlenite, and elution of fluorine can be suppressed by this strutlingite.
Thus, the elution of fluorine can be suppressed by producing a hydrate such as strutlingite and immobilizing fluorine with strutlingite.

Next, the composition of the mixed slag from which gehlenite is generated will be described.
When CaO is less than 34% by mass, the elution from the mixed slag (ease of dissolution) is slightly increased, and the F elution amount is slightly increased. On the other hand, when CaO exceeds 52 mass%, the F elution amount is slightly increased but may increase, and the formation of gehlenite is suppressed, and the fluorine fixation is considered to be insufficient. Therefore, CaO is preferably 34 to 52% by mass.

If the Al ₂ O ₃ content is less than 16% by mass, the F elution amount may increase slightly, but this may increase. This is due to the fact that C ₂ S is increased (C ₂ S rich), thereby generating gehlenite. This is thought to be due to the suppression of Further, when the Al ₂ O ₃ concentration in the slag exceeds 25 mass%, the F elution rate increases as will be described later. Therefore, Al ₂ O ₃ is is preferably 16 to 25 wt%.

If the SiO ₂ content is less than 18% by mass, the F elution amount may be slightly increased but may increase, and the formation of gehlenite is suppressed, and the fluorine fixation is considered insufficient. On the other hand, if SiO ₂ exceeds 26% by mass, the mixed slag is relatively easy to dissolve in water as with the molten iron slag S1, so that the F elution amount is slightly increased. Therefore, SiO ₂ is preferably set to 18 to 26 mass%.

When MgO exceeded 10% by mass, the F elution amount was remarkably increased. When MgO increases, the generation of gehlenite is suppressed, so that the mixed slag is easily eluted, and as a result, the F elution amount increases. Moreover, when the above-mentioned hot metal slag S1 and ladle smelting slag S2 are mixed, the actual situation is that MgO does not fall below 6% by mass from the actual operation.
The remainder is an unavoidable impurity, and a trace amount of inevitable impurities mixed in the molten iron slag S1 and the ladle refining slag S2.

Thus, the amount of F elution can be suppressed by generating gehlenite in the mixed slag. The inventor conducted various experiments paying attention to factors that suppress elution from slag in addition to the generation of gehlenite.
FIGS. 7 to 9 summarize the results of various experiments, and summarize the concentration of Al ₂ O ₃ in the slag and the components that dissolve into the water from the slag.

As shown in FIG. 7 (a), in any slag of hot metal slag S1, ladle smelting slag S2, and mixed slag, the amount of Al elution in the aqueous solution increases as the concentration of Al ₂ O ₃ in the slag increases. doing. As shown in FIG. 7B, as the Al ₂ O ₃ concentration in the slag increases, the rate at which Al is dissolved (Al elution rate) also increases. The Al elution rate is the ratio of Al dissolved in water out of Al contained in the slag.

When the relationship between the Al ₂ O ₃ concentration in the slag and the Ca elution amount was also investigated, as shown in FIG. 8A, as the Al ₂ O ₃ concentration in the slag increases, the Ca in the aqueous solution is increased. The amount of elution is increasing. As shown in FIG. 8 (b), as the concentration of Al ₂ O ₃ in the slag increases, the proportion of Ca melting out (Ca elution rate) also increases. The Ca elution rate is the proportion of Ca dissolved in water out of Ca contained in the slag, like the Al elution rate.

From this, it can be seen that the Al ₂ O ₃ concentration in the slag affects the dissolution of Al and Ca.
Accordingly, the Al ₂ O ₃ concentration in the slag and the fluorine elution amount (F elution amount) were also examined. As shown in FIG. 9A, as the Al ₂ O ₃ concentration in the slag increases, the aqueous solution The amount of elution of fluorine is increasing. As shown in FIG. 9 (b), as the concentration of Al ₂ O ₃ in the slag increases, the rate at which fluorine is dissolved (F elution rate) also increases. In addition, F elution rate is the ratio of F which melt | dissolved in water among F contained in slag similarly to Al elution rate and Ca elution rate.

FIG. 10 summarizes the Al ₂ O ₃ concentration in the slag and the fluorine elution rate in each slag (hot metal slag S1, ladle refining slag S2, mixed slag).
As shown in FIG. 10, when the Al ₂ O ₃ content in the slag exceeds 25% by mass, the F elution rate increases rapidly, so the Al ₂ O ₃ concentration in the slag should be 25% by mass or less. Can suppress the elution of slag.

[About hydration treatment]
As described above, it is possible to suppress the elution of fluorine by suppressing the elution of slag by making it possible to generate gehlenite or by reducing the Al ₂ O ₃ concentration in the slag to 25% by mass or less. In the present invention, further, elution of fluorine is suppressed by producing a hydrate of gehlenite that immobilizes fluorine by performing a hydration treatment on the mixed slag. Specifically, first, after mixing the molten iron slag S1 and the ladle refining slag S2 in a molten state in the waste container 1, the waste container 1 is cooled and the mixed slag is taken out. Then, the mixed slag is finely pulverized and a magnetic separation process for removing Fe is performed. The mixed slag after pulverization, for example, is poured for about 20% by weight of water and allowed to stand for 1 week to form gehlenite hydrate in the mixed slag.

FIG. 11 summarizes the relationship between the hydration treatment and the F elution amount. As shown in FIG. 11, when the hydration treatment is not performed on the mixed slag, the F elution amount exceeds 0.8 mg / L determined by the soil environment standard. On the other hand, when the hydration treatment is performed on the mixed slag, the F elution amount can be reduced to 0.8 mg / L or less which is the soil environment standard, and in particular, the amount of water is large and the hydration treatment time is long. In this case, the F elution amount can be suppressed.
[Example]
Next, the steelmaking conditions (steelmaking implementation conditions) until the production of recycled slag and the implementation conditions (recycled production implementation conditions) for producing recycled slag are described.

  The waste container 1 for charging the slag was provided with countermeasures against deformation so that it would not be deformed even if the slag was received several times, and used on the carriage so that it could be transported and tilted. The waste container 1 was made of cast steel containing C = 0.2 mass%, Si = 0.3 mass%, and Mn = 0.6 mass%. The inner wall of the waste container 1 is coated with the molten iron slag S1, and then the ladle smelting slag S2 is received several times, and when the ladle smelting slag S2 is fully loaded, the slag is moved to the slag draining area. I let you.

  In the operation of the blast furnace, hot metal was made by adding raw materials such as pellets, iron ore, coal, coke and lime from the upper part of the blast furnace as usual by those skilled in the art. Air was blown from the side of the blast furnace and hot metal was discharged. After unloading from the blast furnace, the hot metal and the blast furnace slag were separated using a skin marker (specific gravity separation weir) provided on the blast furnace casting floor, and the separated blast furnace slag was discharged into the waste container 1. In this embodiment, only the blast furnace slag is discharged into the waste container 1 as the molten iron slag S1.

Further, for the molten iron, CaO or FeO was added to lower the Si in the hot metal depending on the steel type, and the hot metal was desiliconized. In addition, if it is in the range of the composition mentioned above, after the blast furnace desiliconization slag used for the desiliconization treatment is discharged into the discharge vessel 1 like the blast furnace slag, it is mixed with the ladle refining slag S2. Slag may be generated.
Blast hearth desiliconization slag generated during desiliconization treatment was also charged into the waste container 1. The molten iron after desiliconization is charged into a ladle or a kneading car (topy car) and blown as usual by those skilled in the art to remove impurities such as Si, P, and S (preliminary hot metal treatment) Went. In addition, if it is in the range of the composition mentioned above, the hot metal preliminary treatment slag generated in the hot metal preliminary treatment is also mixed with the ladle refining slag S2 after being discharged into the waste container 1 like the blast furnace slag. Slag may be generated.

After the hot metal slag S1 (blast furnace slag, blast furnace desiliconization slag, hot metal pretreatment slag) is discharged into the waste container 1, it is discharged to the outside in a molten state, whereby the inner wall of the waste container 1 (iron The inner wall of the skin) is coated with hot metal slag S1. The molten iron slag S1 discharged to the outside is reused as a concrete material after being granulated and dried.
The hot metal discharged from the blast furnace or the hot metal after the hot metal pretreatment is blown (primary refining) in a converter or the like as usual by those skilled in the art, and then the molten steel is discharged into the ladle. During primary refining, alloys are added as necessary, and alloys are added at the time of molten steel production. For example, calcined lime and synthetic flux are added at a predetermined ratio at the time of steel output so that the total amount of input becomes 1.3 to 7.0 kg / t. For calcined lime (quick lime), for example, CaO: 96 mass%, Mg 0: 1 mass%, SiO ₂ : 1 mass%, and others: 2.0 mass% were used. When charging calcined lime, in order to facilitate melting, the synthetic flux was first added, and then calcined lime was added.

At this time, for the synthetic flux, a pre-melt material was used in order to further improve the hatchability (to some extent after steel is released). The synthetic flux is CaO: 45 to 49% by mass, Al ₂ O ₃ : 36 to 40% by mass, SiO ₂ : 4% by mass or less, MgO: 12 to 17% by mass, TiO ₂ : 0.1% by mass or less And slag having a higher fluorine content than usual was used so that the effect of suppressing the F elution amount could be understood. When using the synthetic flux, it was used after confirming whether the composition was in the above range by JIS G1258 “ICP emission spectroscopic analysis method”.

About the ladle which receives molten steel, the cylindrical thing of the range whose aspect ratio is 0.8-1.2 was used. MgO-C refractory brick was used as the refractory for the ladle. The refractory brick, MgO: 75 wt%, FC: 15 wt%, Al ₂ O _3: 6 wt%, Other: was used in 2.0 mass%. The use of slag line MgO-C refractories is described in "Ladle Refining Method, Technology that Supports the Development of the Ladle Refining Method p241 Supervised by the Iron and Steel Institute of Japan, Hiroyuki Tsujioka, 1997, Jinjinsha" In general, the composition of the MgO—C material is not limited to that described above.

  The ladle used was 90 ton class. The ladle should be used continuously after receiving the molten steel before the surface temperature of the ladle has dropped below about 1000 ° C (continuous use in the hot), or Prior to receiving steel, the ladle was warmed in advance and then the molten steel was received. Use of preheating is, for example, after the construction of the refractory, the surface temperature is heated to 1000 ° C or higher and then the molten steel is received (new pan heating method), and after the molten steel is discharged, the surface temperature is once less than 1000 ° C. There is a method (discontinuous method) in which molten steel is received after reheating it to 1000 ° C or higher for the ladle that has become, and both the new heating method and the discontinuous method are applied depending on the operating situation did.

After the primary refining in the converter, the molten steel is taken out into the ladle and the ladle is moved to the secondary refining equipment (secondary refining process). In the secondary refining, for example, the arc heating method as usual in the art Using the secondary refining device (LF device), the temperature or component adjustment treatment of the molten steel was performed. In secondary refining, vacuum degassing was performed as necessary to stabilize dissolved oxygen remaining in the molten steel. Vacuum degassing is a process for dehydrogenating molten steel by evacuating steel types that require lower hydrogen, such as alloy steel, and reducing the oxygen level in the steel like clean steel. This process is also performed when huge inclusions are reduced. By stirring the molten steel under vacuum, Al ₂ O ₃ in the molten steel is adsorbed on the slag.

In the LF apparatus, as described above, deoxidation was performed on molten steel by introducing Al. Moreover, in LF apparatus, the molten steel was heated to 1500-1650 degreeC (liquidus temperature +50 degree | times or more), and after mixing adjustment, sufficient stirring was performed and the molten steel was conveyed to the continuous casting apparatus.
In the continuous casting apparatus, casting was performed by injecting molten steel into a tundish through a ladle and then charging the molten steel into a mold as usual by those skilled in the art. The ladle that completed the pouring of the molten steel into the tundish was drained and discarded, and then the ladle was prepared as usual by those skilled in the art.

After pouring the molten steel from the ladle into the tundish, the ladle refining slag S2 remaining in the ladle and part of the molten steel are discharged into the waste container 1 coated with the molten iron slag S1, and the molten iron slag S1 and ladle refining slag S2 reacted to produce mixed slag.
The ladle smelting slag S2 to the waste container 1 was repeated until the waste container 1 was full. When the waste container 1 became full (full), the waste container 1 was replaced with a new one. In addition, when the waste container 1 is coated with the molten iron slag S1, it is possible to prevent the molten steel from being seized into the waste container 1.

The slab (steel slab) after continuous casting is subjected to partial rolling, and oxygen analysis is cut out at D / 8 of the steel slab and quantitative analysis is performed according to JIS Z 2613 “General Rules for Oxygen Determination of Metallic Materials” It was. The steel type was evaluated for S45C.
Immediately after hot ladle slag S2 is mixed with hot metal slag S1, the molten slag is cooled (solidified) from the viewpoint of preventing a steam explosion since molten steel and the like are present in a molten state in the waste container 1. ) And discharged to the outside. After discharging the mixed slag, crushing, water cooling (hydration treatment), magnetic separation, and air cooling are performed. Fluorine is measured based on the dissolution test method in accordance with the Environmental Agency Notification No. 46, which is a verification method for soil environmental standards. did. In addition, the upper limit of the elution amount of fluorine is 0.8 mg / L or less based on the standard (soil environmental standard) shown in Article 16 paragraph 1 of the Environmental Basic Law (1993 Law No. 91).

The mixed slag that satisfied the elution amount of fluorine was shipped as material for earthwork and roadbed materials. Some of the mixed slag was crushed and sorted, adjusted in particle size or granulated, and reused as a CaO source for secondary refining. The empty waste container 1 received hot metal slag S1 again and was used repeatedly.
About hot metal slag S1, ladle smelting slag S2, and mixed slag, it analyzed about the component and the amount of elution by the ion chromatograph method or the high frequency inductively coupled plasma emission spectroscopic analysis method as usual by those skilled in the art.

In addition, in order to evaluate how the elution amount of fluorine changes depending on the presence or absence of hydration treatment, first, mixed slag that has been subjected to hydration treatment in which 20% water is applied and left to stand for one week. And a second pattern for performing the fluorine elution test on the cooled mixed slag as it is.
Furthermore, in order to make a comparison between the case where hot metal slag S1 and ladle refining slag S2 are mixed hot and the case where heat mixing is not performed, hot metal slag S1 after cooling and ladle refining after cooling are performed. After mixing with slag S2, the pattern which performs the elution test of a fluorine about the mixed slag was also added.

The fluorine elution test is in accordance with Ministry of the Environment Notification No. 6. For example, after 50 g of slag was diluted 10 times with 450 g of water and hydrated and eluted for 6 hours, the concentration of fluorine in the filtered water was determined by ion chromatography. Measurements were made using the graph method.
Table 2 shows an example in which recycled slag was produced by the method for producing recycled slag according to the present invention based on the above-described implementation conditions, and the production of recycled slag by a method different from the method for producing recycled slag according to the present invention. The comparison example performed is shown.

In Comparative Examples 1 and 12, since the basicity of the ladle refining slag S2 was less than 3, the refining performance of the molten steel was lowered, and the oxygen level in the steel could not be reduced to 9 ppm or less by secondary refining ( Column of molten steel processability, refining x). In addition, in Comparative Examples 1 and 12, since Al ₂ O ₃ of the mixed slag is less than 16% by mass and SiO ₂ exceeds 26% by mass, the F elution amount is an environmental standard (soil environmental standard). It could not be reduced to 0.8 mg / L or less (column of fluorine elution amount).

In Comparative Examples 2, 10, 13, and 20, the Al ₂ O ₃ content in the ladle refining slag S2 exceeds 48% by mass, so the ability to adhere and remove Al ₂ O ₃ inclusions in the molten steel is reduced. In the next refining, the oxygen level in the steel could not be reduced to 9 ppm or less.
In Comparative Examples 5 and 16, the ladle refining slag S2 has a SiO ₂ content of more than 16% by mass and exceeds the liquidus at 1500 ° C., so the refining ability by the slag is reduced, and the steel is obtained by secondary refining. The oxygen level could not be reduced below 9 ppm.

  In Comparative Example 22, since the MgO of the ladle refining slag S2 exceeds 11% by mass, the fluidity of the slag was deteriorated, and the oxygen level in the steel could not be reduced to 9 ppm or less by secondary refining. In addition, in Comparative Example 22, since MgO of the mixed slag exceeds 10% by mass, generation of gehlenite is suppressed, and as a result, the F elution amount is set to 0.8 mg / L or less which is an environmental standard. Could not be done (column of fluorine elution amount).

  In Comparative Example 25, since CaO of the mixed slag exceeds 52% by mass, gehlenite is not sufficiently generated (presence of gehlenite hydrate), and the F elution amount can be 0.8 mg / L or less. There wasn't. In Comparative Example 26, since the CaO of the mixed slag was less than 34% by mass, the slag elution was slightly increased, and the F elution amount could not be reduced to 0.8 mg / L or less.

In Comparative Example 27, since Al ₂ O ₃ of the mixed slag exceeded 25% by mass, the elution of the lag became slightly high, and the F elution amount could not be reduced to 0.8 mg / L or less. In Comparative Example 28, Al ₂ O ₃ of the mixed slag was less than 16% by mass, so that gehlenite was not sufficiently generated, and the F elution amount could not be reduced to 0.8 mg / L or less.
In Comparative Example 29, since the SiO _{2 of} the mixed slag exceeds 26% by mass, the mixed slag is easily dissolved in water like the molten iron slag S1, and the F elution amount may be 0.8 mg / L or less. could not. In Comparative Example 30, since the SiO _{2 of} the mixed slag was less than 18% by mass, gehlenite was not sufficiently generated, and the F elution amount could not be reduced to 0.8 mg / L or less.

In Comparative Example 31, since MgO of the mixed slag exceeds 10% by mass, the generation of gehlenite is suppressed, and as a result, the F elution amount cannot be reduced to 0.8 mg / L or less.
Since the comparative example 32 was only ladle refining slag S2 without mixing molten iron slag S1, gehlenite was not fully produced | generated and F elution amount was not able to be 0.8 mg / L or less.

  In Comparative Examples 33 and 34, the mixed slag was hydrated, but when mixed slag was produced by mixing the molten iron slag S1 and the ladle smelting slag S2, it was not mixed hot (slag slag). Because of this, no hydrate of gehlenite was produced (no gehlenite that suppresses fluorine). As a result, the F elution amount could not be reduced to 0.8 mg / L or less.

In Comparative Examples 35 and 36, since no hydration treatment was performed, the hydrate of gehlenite that immobilizes fluorine was not sufficient, and the F elution amount could not be reduced to 0.8 mg / L or less.
In Comparative Examples 37 and 38, the hot metal slag S1 and the ladle smelting slag S2 were not mixed hot, and no hydration was performed, so that the F elution amount could be 0.8 mg / L or less. There wasn't.

  In the embodiment disclosed herein, matters not explicitly disclosed, for example, operating conditions, various parameters, dimensions, weights, volumes, etc. of the components do not deviate from the range normally practiced by those skilled in the art. However, matters that can be easily assumed by those skilled in the art are employed.

1 Waste container S1 Hot metal slag S2 Ladle refining slag S3 Recycled slag

Claims (1)

When manufacturing recycled slag,
Chemical composition, CaO: 24 to 50 wt%, Al ₂ O _3: 1~16 wt%, SiO _2: 17-38 wt%, MgO: 0.3 to 10 A% by mass balance be unavoidable impurities And the hot metal slag which becomes CaO / SiO ₂ : 1-2 is put into the waste container, and the inner surface of the waste container is coded by the hot metal slag,
The chemical components are CaO: 33 to 66% by mass, Al ₂ O ₃ : 22 to 48% by mass, SiO ₂ : _{3 to} 16% by mass, MgO: 5 to 11% by mass, the balance being inevitable impurities and CaO / SiO ₂ : Ladle smelting slag of 3 or more is charged in a molten state into a waste container coated with the molten iron slag,
The chemical components of the mixed slag mixed are CaO: 34 to 52% by mass, Al ₂ O ₃ : 16 to 25% by mass, SiO ₂ : 18 to 26% by mass, MgO: 6 to 10% by mass, and the remainder is inevitable. To be impurities,
A method for producing recycled slag, wherein the mixed slag is hydrated after cooling.