JP5444883B2 - Modified slag - Google Patents

Description

The present invention provides a steelmaking slag treatment method in which a steelmaking slag is melt-modified and reduced by adding a SiO ₂ -containing reforming material and a reducing carbon source while heating the steelmaking slag with a heating means, and a modification obtained by this treatment. Concerning quality slag.

  The steelmaking slag generated in the refining process of the steelmaking process such as the hot metal pretreatment and the decarburization process contains free CaO (hereinafter referred to as “f · CaO”), and its volume is increased by the hydration reaction of this f · CaO. It may expand and create many microcracks and open pores. Such a steelmaking slag containing a large amount of f · CaO has low volume stability. In addition, the steelmaking slag in the molten state (the state having fluidity) contains many bubbles mainly composed of CO gas. When the molten steelmaking slag containing many bubbles is cooled, the steelmaking slag is solidified in the state containing the bubbles. Therefore, the quality is low.

  Therefore, steelmaking slag is used exclusively for low-grade applications such as temporary construction materials for civil engineering, road ground improvement materials, lower-layer roadbed materials, etc., and for higher-grade applications such as upper-layer roadbed materials, concrete aggregates, and stone raw materials. It is difficult to use.

  On the other hand, in order to effectively use steelmaking slag for high-grade applications as described above, steelmaking slag is reduced by reducing f · CaO in steelmaking slag or by reducing bubbles in molten steelmaking slag. The quality of slag is being improved and the product value is being increased.

For example, in Patent Document 1, a SiO ₂ -containing modifier is added to lower the basicity, and a carbon source for reduction is added to reduce the amount of iron oxide to generate bubbles mainly composed of CO gas. Inhibiting is described. Patent Document 1 also describes that a substance containing at least one of SiO ₂ , Al ₂ O ₃ , and MgO is added to lower the melting temperature of the slag.

Further, for example, in Patent Document 2, in order to reduce the concentration of oxides such as iron oxide and P ₂ O _{5 in the} slag, the indentation depth L _S of the steelmaking slag by oxygen blown from the lance and the steelmaking slag are disclosed. The ratio L _S / L _S0 to the thickness L _S0 is limited to a predetermined range. Patent Document 2 also describes that a modifying material further containing Al ₂ O ₃ may be used as the modifying material.

JP 2007-297893 A JP 2007-297694 A

By the way, according to the study by the present inventors, when a modifier containing a predetermined amount or more of Al ₂ O ₃ is added, the reduction rate of oxides such as iron oxide and P ₂ O ₅ by the reducing carbon source is improved. However, it has been found that if the concentration of Al ₂ O ₃ becomes too high, the viscosity of the slag during the melt reforming reduction treatment increases, and conversely the reduction rate decreases. Further, in this case, separation of carbon and slag in the carbon source for reduction added during the melt reforming process is hindered, and the carbon remains in the slag after treatment. It has also been found that this leads to a decrease in strength.

On the other hand, Patent Document 1 and Patent Document 2 describe that a modifier containing Al ₂ O ₃ is added, but an appropriate addition amount is not specified.

Therefore, the present invention has been made in view of such circumstances, and in a steelmaking slag treatment method for subjecting steelmaking slag to a melt reforming reduction treatment, and a modified slag obtained by this treatment, an appropriate Al ₂ O ₃ content can be obtained. By defining the addition amount, it is an object to improve the steel reduction slag with high density and high strength while improving the reduction rate of oxides such as iron oxide and P ₂ O ₅ in the steelmaking slag.

As a result of intensive studies to solve the above problems, the present inventors have added an Al ₂ O ₃ -containing substance so that the Al ₂ O ₃ concentration in the steelmaking slag becomes a predetermined concentration through the melt reforming reduction treatment. In addition to determining the amount, the addition amount of the SiO ₂ -containing modifier is determined so that the basicity of the steelmaking slag after the melt reforming reduction treatment is not less than a predetermined value, so that iron oxide and P in the steelmaking slag can be obtained. It has been found that a steelmaking slag with high density and high strength can be obtained while improving the oxide reduction rate of ₂ O ₅ or the like, and the present invention has been completed based on this finding.

According to the present invention, the steel slag hot metal is charged to the reaction vessel which is held with heating in a heating means using oxygen gas, SiO ₂ content modifier and a carbon source for the reduction in the steelmaking slag The modified slag obtained by subjecting the steelmaking slag to a melt reforming reduction treatment, wherein the Al ₂ O ₃ concentration in the reformed slag is 7% by mass or more and 20% by mass or less. and the basicity of the slag is 0.7 or more, the S concentration in the reformed slag Ri der than 0.7 wt%, the concentration of total iron in the reformed slag is not more than 1 wt%, modified Quality slag is provided.

  Furthermore, the MgO concentration in the modified slag is preferably 15% by mass or less.

According to the present invention, in a steelmaking slag treatment method for subjecting steelmaking slag to a melt reforming reduction treatment and a reformed slag obtained by this treatment, the concentration of Al ₂ O ₃ in the steelmaking slag is a predetermined concentration through the melt reforming reduction treatment. with the addition of Al ₂ O ₃ containing substance such that, by adding SiO ₂ containing modifier as basicity of the steel slag after melting reforming reduction treatment is equal to or greater than a predetermined value, modification reduction Decreasing the viscosity of steelmaking slag during processing, thereby improving the reduction rate of oxides such as iron oxide and P ₂ O _{5 in} steelmaking slag, and obtaining a refined steelmaking slag with high density and high strength Is possible.

It is a graph which shows an example of the relationship between the basicity of steelmaking slag after a reforming reduction process, and compressive strength (N / mm < ² >). Is a graph showing an example of the relationship between reduction rate of the concentration of Al ₂ O ₃ steelmaking slag in the reforming reduction treatment (mass%) and iron oxide (FeO). Is a graph showing an example of the relationship between the reforming concentration of Al ₂ O ₃ compressive strength of steel slag after (mass%) and modified reduction treatment steelmaking slag during reduction treatment (N / mm ^2).

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[About the steel slag treatment method according to the present invention]
First, an outline of the steel slag treatment method according to the present invention will be described. The steelmaking slag treatment method according to the present invention is a method of adding a SiO ₂ -containing modifier and a reducing carbon source to a steelmaking slag while heating the steelmaking slag with a heating means, and subjecting the steelmaking slag to a melt reforming reduction treatment. is there. That is, in the steelmaking slag treatment method according to the present invention, the steelmaking slag is charged into the reaction vessel and then heated and melted by using a heating means, and the SiO ₂ -containing modifier and reducing carbon The source is added and the steelmaking slag is reformed and reduced in the molten state. The steelmaking slag is charged into a reaction vessel in which hot metal is held as seed hot water. Hereinafter, each item regarding such a steelmaking slag processing method according to the present invention will be described in detail.

(Types of steelmaking slag)
In the present invention, steelmaking slag is subject to reforming treatment, and the steelmaking slag to be reformed is not particularly limited. For example, decarburization slag, hot metal pretreatment slag, electric furnace slag, or the like is used. Can do.

(Status of slag being processed)
In the present invention, as described above, the steelmaking slag is melted by the heating means, and the reforming process and the reduction process are performed in a state where the steelmaking slag is melted. The reason why the treatment is performed in the molten state is that it is effective that the slag to be treated is in a molten state in order to promote the f · CaO hatching (melting homogenization) and the reduction reaction of the slag. . Hereinafter, this point will be described in more detail.

(Improvement of steelmaking slag)
By adding a SiO ₂ -containing modifier to the molten steelmaking slag and performing a reforming treatment, unreacted f · CaO in the steelmaking slag is hatched, and the hatched f · CaO and SiO ₂ are By this reaction, f · CaO can be reduced. Therefore, volume expansion due to the hydration reaction of f · CaO (Ca + 2H ₂ O → Ca (OH) ₂ + H ₂ ) can be prevented. Here, the reforming process is performed in a molten state when the reforming process is performed at a temperature lower than the melting temperature, unsaturated slag remains as a solid phase before the process, and a high melting point precipitate is formed as the solid phase. This is because a phase may remain, so that the reaction with SiO ₂ does not proceed sufficiently, and f · CaO cannot be reduced stably.

  The “molten state” in the present invention may be in a state having fluidity, and does not necessarily need to be completely in a liquid phase before the start of the reforming and reducing treatment. As a specific index, when expressed by an estimated value obtained from a slag composition by commercially available thermodynamic calculation model software (for example, SOLGASMIX), the liquid phase ratio may be 30% or more. As the reforming and reduction treatment progresses, the solidity ratio decreases due to a decrease in basicity due to heating or thermal spraying of the reforming material. As a result, the fluidity of the slag is further improved and the reforming and reduction treatment is promoted. .

(Reduction treatment of steelmaking slag)
In the present invention, the iron oxide in the steelmaking slag is reduced by reducing the steelmaking slag in the molten state (thereby reducing the total iron (hereinafter referred to as “T.Fe”)). ), Generation of bubbles mainly composed of CO gas can be prevented. The CO gas bubbles are suspended in granular iron in a molten steelmaking slag immediately after being discharged from a converter or the like (hereinafter sometimes referred to as “molten slag”). It is generated when carbon contained in granular iron reacts with iron oxide in molten slag. Therefore, the generation of CO gas can be prevented by reducing the amount of iron oxide as an oxygen source by reducing the iron oxide in the molten slag.

In the present invention, the T. slag in the steelmaking slag is also obtained by reducing the steelmaking slag in a molten state. By reducing Fe, the appearance of the slag can be whitened or transparent to improve the appearance, and the slag can have high added value. The slag When there is much Fe, it is black, but FeO and Fe ₂ O ₃ in the slag are reduced to reduce T.I. When Fe is reduced, the slag after the reduction treatment can be decolorized to be close to white or transparent. In this way, T.W. If the steelmaking slag having a large amount of Fe and blackened can be whitened or made transparent and mixed with cement as a concrete aggregate, the use of the steelmaking slag after the reduction treatment can be remarkably expanded. For that purpose, it is necessary to make it whiter than cement or whiter than cement. This is because when black slag stronger than cement is mixed as an aggregate, it appears as a black dot in the concrete and the appearance is impaired.

  Specifically, according to the results of experiments conducted by the present inventors, T.O. When the Fe concentration is 1.5% by mass or less, even if it is mixed with ordinary Portland cement as an aggregate, the appearance of the cement is not impaired, which is preferable. T. When Fe is reduced to 0.5% by mass or less, the whiteness of the white cement is comparable to that of white cement and can be used as an aggregate of white cement, which is a higher-grade application. It is particularly preferable that Fe be 0.5% by mass or less.

Moreover, in this invention, valuable components, such as iron, phosphorus, and manganese, in steelmaking slag can be collect | recovered by performing the reduction process of steelmaking slag in a molten state. Steelmaking slag contains a large amount of valuable metals such as iron, phosphorus and manganese in the form of oxides (FeO, MnO, P ₂ O ₅ etc.) in addition to CaO and SiO ₂ . Therefore, when hot metal is used as a seed bath, the oxides of these valuable components are reduced by adding a carbon source for reduction into the steelmaking slag, and valuable components such as iron, phosphorus and manganese are reduced. It can be recovered in the hot metal.

In particular, phosphorus is important because it is used as a fertilizer raw material. Generally, since phosphorus causes brittleness of iron, it is usually removed from the hot metal by dephosphorization treatment, but the present invention temporarily concentrates phosphorus in the seed hot water, and then high concentration. The hot metal containing phosphorus is dephosphorized, recovered as high-concentration phosphorus oxide (P ₂ O ₅ ) in the obtained slag, and used as a fertilizer raw material or the like.

  In addition, for example, by performing the reduction treatment of the present invention repeatedly using the same seed hot metal, and dephosphorizing after increasing the phosphorus concentration in the hot metal, dephosphorization slag containing high concentration phosphorous oxide is generated. It is possible. Such dephosphorization slag becomes a high-quality phosphorus resource capable of recovering phosphorus from a small amount of slag with high efficiency.

(Role of seed hot metal)
In the present invention, the molten steelmaking slag is charged into a reaction vessel in which hot metal as seed hot water is held. As a result, in the reforming reduction reaction of steelmaking slag, not only the sensible heat of molten steelmaking slag but also the sensible heat of seed hot metal can be used, and the slag once melted during the reduction reaction, which is an endothermic reaction, is in a molten state Can be maintained. As a result, as described above, the hatching of f · CaO in the slag can be promoted, the reduction rate of the slag can be maintained, and the degassing rate of CO can also be maintained. Here, from the viewpoint of maintaining the molten state of the slag during the reduction reaction (endothermic reaction) by utilizing the sensible heat of the hot metal, the mass of the seed hot metal is ¼ or more of the mass of the steelmaking slag. It is preferable that it is the same mass or more as steelmaking slag, and it is most preferable that it is 1.5 times or more of the mass of steelmaking slag. When the mass of the hot metal is less than 1/4 with respect to the mass of the steelmaking slag, the temperature of the slag is reduced during the reduction reaction, and it becomes difficult to maintain the molten state of the slag. It is preferable that it is 1/4 or more with respect to the mass of steelmaking slag.

  Moreover, by using hot metal as seed hot water, the hot metal / slag interface can be used as a site for the reduction reaction. The reduction reaction of steelmaking slag proceeds mainly at the hot metal / slag interface rather than the slag / reducing carbon source interface. In other words, the reduction reaction rate is greater at the hot metal / slag interface than at the slag / reducing carbon source interface, so by introducing the steelmaking slag into a container holding the hot metal, the hot metal / slag interface is used as the reduction reaction site. By utilizing this, the reduction reaction rate of steelmaking slag can be increased (reduction reaction is promoted). Here, in the case where the hot metal / slag interface is used as the reduction reaction site, in order to maximize the reduction reaction rate, from the viewpoint of maximizing the reduction reaction interface area, the amount of hot metal used as the seed bath is at least the reaction It is preferable that the amount covers the entire bottom surface of the container.

  Furthermore, by using hot metal as the seed hot water, valuable components (iron, phosphorus, manganese, etc.) in the steelmaking slag can be recovered with high efficiency in the hot metal using the seed hot water. The valuable metal oxides such as phosphorus and manganese in the steelmaking slag are reduced to become a single metal and transferred to the seed hot metal. As described above, from the viewpoint of maximizing the reduction reaction interface area, the seed hot metal is retained in a large amount in the reaction vessel in order to cover at least the entire bottom surface of the reaction vessel. Therefore, even if valuable components such as phosphorus and manganese in steelmaking slag are transferred to a large amount of seeded hot metal, the concentration of valuable components in the seeded hot metal is low. The transition rate, in other words, the reduction rate of the valuable component oxide in the steelmaking slag can be maintained until the valuable component concentration reaches saturation. On the other hand, when the amount of the seed hot metal is small, the concentration of valuable components such as phosphorus and manganese is likely to be saturated, so that the reduction rate of the valuable component oxide is reduced.

(Heating means)
In the present invention, a heating means such as a heating burner (hereinafter referred to as “burner heating means”) or a combustion means is used as the heating means in order to maintain the same processing temperature during the reforming treatment and the reduction treatment. It is preferable to use a heating means (hereinafter referred to as “heating means using oxygen gas”) by blowing oxygen with a lance or the like while supplying the carbonaceous material. Here, as the fuel for the heating burner, for example, heavy oil, liquefied petroleum gas (LPG), or the like can be used. In the case of a heating means using oxygen gas, the steelmaking slag is heated using combustion heat generated when the combustion carbonaceous material is burned. The combustion carbonaceous material may be in the same form or different form from the reducing carbon source used for the reduction treatment of the steelmaking slag. Further, both the combustion carbon material and the reducing carbon source may be supplied from the same heating means, for example, a powder thermal spray burner, and from different heating means, for example, the combustion carbon material may be powder thermal sprayed. The carbon source for reduction may be supplied from a burner, and may be supplied from a pipe installed on the upper surface side of the slag different from the powder sprayed burner.

  Here, among the heating means using the burner heating means and oxygen gas, as will be described in detail later, in order to solve the problem of yellow water generation that occurs in the case of blast furnace slag, In order to make the sulfur (S) concentration in 0.7) mass%, it is preferable to use a heating means using oxygen gas as the heating means.

(Soaking of slag by gas stirring)
Further, during the reforming and reducing treatment, the heating as described above is performed from the upper surface side of the slag, so that the reforming reaction and the reduction reaction sufficiently proceed on the upper surface side of the slag, while the upper surface of the slag is on the lower surface side of the slag (hot metal side). Since the effect of heating from the side is difficult to achieve, the reforming reaction or reduction reaction may not proceed sufficiently. Therefore, in order to equalize the steelmaking slag during the reforming reduction treatment, gas may be blown into the steelmaking slag from an upper blowing lance or the like to stir the slag being treated. As the gas species used for such stirring, for example, an inert gas such as argon can be used. However, when a combustion carbon material is supplied to the slag, a gas containing oxygen as the stirring gas. Since the oxygen-containing gas for stirring can burn the combustion carbonaceous material, the slag temperature can be efficiently maintained simultaneously with the slag stirring.

(Modified material containing SiO ₂ )
In the present invention, the SiO ₂ -containing reforming material is added to the steelmaking slag in order to reduce the basicity of the steelmaking slag (CaO / SiO ₂ mass ratio) in the reforming treatment. Such a SiO ₂ -containing modifying material is not particularly limited as long as it contains silicic acid, but those having a SiO ₂ content of 50% by mass or more are preferable. For example, coal ash, silica sand Etc. can be exemplified. In addition, with respect to the SiO ₂ -containing modifier, the remainder of the SiO ₂ component is often mainly an Al ₂ O ₃ component. Further, the size of the SiO ₂ -containing modifier is not particularly limited.

Here, in the present invention, it is necessary to adjust the addition amount of the SiO ₂ -containing modifier so that the basicity of the steelmaking slag after the reforming reduction treatment is 0.7 or more. Hereinafter, the reason why the basicity of the steelmaking slag after the reforming reduction treatment is set to 0.7 or more will be described with reference to FIG. FIG. 1 is a graph showing an example of the relationship between the basicity of steelmaking slag after the reforming reduction treatment and the compressive strength (N / mm ² ).

  The present inventors conducted the following experiment in order to examine the appropriate basicity of the steelmaking slag after the reforming reduction treatment.

First, 5 to 10 mm diameter coal ash used as a SiO ₂ -containing modifier, and 5 to 20 mm diameter alumina used as an Al ₂ O ₃ containing substance in a converter reactor holding 100 t of hot metal seed 3.3 to 10 mm diameter coke 3.3t used as a system refractory scrap and a carbon source for reduction was charged in advance. Thereafter, the hot metal pretreatment slag 20t was charged into the converter reactor in a molten state. The input amount of coal ash was used as a variable in order to obtain slag after the reforming reduction treatment with changing basicity. In addition, for the alumina-based refractory waste, the amount required to make the Al ₂ O ₃ concentration in the slag after the reforming reduction treatment 15% by mass was determined from the amount of coal ash input and the hot metal pretreatment slag composition. .

  Moreover, coke was made into the addition amount which becomes 15 mass% in an external number with respect to 100 mass% of hot metal pretreatment slag charged into the converter reactor in conversion to carbon content.

After charging the slag, oxygen was supplied from the top blowing lance, and the melt reforming reduction treatment was performed for 18 minutes. The treatment temperature was 1400 ° C. to 1470 ° C., and the slag during the treatment was always kept in a molten state. In addition, 10-50 mm diameter coke was continuously supplied from the upper side of the reaction vessel during the melt reforming reduction treatment in order to supplement the carbon consumed by the combustion with the top blown oxygen and the reduction of the iron oxide in the slag. . Regarding the coke supply rate at this time, the amount Q (Nm ³ / h) of exhaust gas generated by the melt reforming reduction treatment and the CO concentration and CO ₂ concentration (volume%) in the exhaust gas were continuously measured. Based on the value, it was determined from the following equation. The CO concentration and CO ₂ concentration in the exhaust gas can be measured by sampling the exhaust gas from the exhaust gas duct connected to the reaction vessel and using an analytical instrument such as a mass spectrometer, an infrared gas analyzer, or a gas chromatography. .
Coke supply speed (kg / h)
_{= (% CO +% CO 2} ) /100×Q/22.4×12/ ( carbon ratio in the coke)
(“% CO” and “% CO ₂ ” represent the CO concentration and CO ₂ concentration (volume%) in the exhaust gas, respectively.)

  After completion of the melt reforming reduction treatment, the treated reforming slag was discharged into a slag pan and solidified.

In addition, as an analysis method of the slag composition in this experiment, fluorescent X-ray analysis is performed according to JIS K 0119, and the compressive strength of the steelmaking slag after the reforming reduction treatment is measured according to JIS A 1132. did. The measurement results are shown in Table 1 below. As a result of this experiment, it was found that the basicity and compressive strength (N / mm ² ) of the steelmaking slag after the reforming reduction treatment have a relationship as shown in FIG.

Incidentally, CaO / slag components other than SiO _{2 is,} Al ₂ O 3 = _14~16 wt%, MgO = 5 to 7 wt%, T. Fe = 0.2 to 0.5 mass% and MnO = 0.9 to 1.5 mass%.

  As a result of this experiment, as shown in FIG. 1, it was found that when the basicity of the steelmaking slag after the reforming reduction treatment is less than 0.7, the compressive strength of the slag tends to be abruptly lowered. This is because, when the basicity of the steelmaking slag after the reforming and reducing treatment is less than 0.7, the viscosity of the slag is high, and when the slag is discharged from the reaction vessel after the reforming and reducing treatment is completed, a reducing carbon source is involved. It is estimated that the strength of the slag is reduced because the carbon remains in the slag without separation of the slag and carbon, and the remaining carbon particles become the starting point of cracks etc. Is done.

Therefore, in the steelmaking slag treatment method according to the present invention, the SiO ₂ -containing modifier is added so that the basicity of the steelmaking slag in the reforming reduction treatment is in the range of 0.7 or more.

  As shown in FIG. 1, in the method for melt reforming and reducing steelmaking slag according to the present invention, the strength of the reformed slag can be increased. For example, upper-layer roadbed materials, concrete aggregates, stone raw materials (wariishi stone, etc.) ), A steelmaking slag having a quality that can be sufficiently used for high-grade applications such as abrasive sand can be obtained.

Further, as the basicity of the steel slag after modification reduction treatment is 1.5 or less, it is preferable to adjust the addition amount of SiO ₂ containing modifier. When basicity of the steel slag exceeds 1.5, the melting point of the slag is increased, the reaction from the viscosity of the slag is increased, the SiO ₂ of the f · CaO and SiO ₂ containing modifier in slag This is because it does not proceed sufficiently and it becomes difficult to stably reduce f · CaO. Furthermore, since the reforming reaction can be performed more reliably when the basicity is lower, the basicity of the SiO ₂ -containing reforming material is adjusted so that the basicity of the steelmaking slag after the reforming reduction treatment is 1.4 or less. It is more preferable to adjust the addition amount.

(Al ₂ O ₃ containing material)
In the steelmaking slag treatment method according to the present invention, it is necessary to add an Al ₂ O ₃ -containing material to the molten steelmaking slag. Such an Al ₂ O ₃ -containing substance is not particularly limited as long as it contains alumina, and examples thereof include coal ash, bauxite, red mud, and alumina refractory waste. According to the study by the present inventors, the viscosity of the steelmaking slag is reduced in the reforming reduction treatment by adding the Al ₂ O ₃ -containing substance, and thereby iron oxide, P ₂ O _5, etc. in the steelmaking slag can be reduced. It is added to improve the reaction rate of the oxide reduction reaction and to shorten the time required for the reforming reduction treatment of the steelmaking slag.

However, it has also been found by the present inventors that if the concentration of Al ₂ O ₃ becomes too high, the viscosity of the slag during the reforming and reduction treatment increases again, and conversely reduces the reduction rate. Therefore, if the concentration of Al ₂ O ₃ becomes too high, the time required for the reforming reduction treatment increases, and accordingly, the energy intensity for heating and the like increases and the amount of CO ₂ generated also increases. The problem that it ends up occurs. Furthermore, since the reduction rate of the oxide in the steelmaking slag is reduced, T.I. There are also problems that Fe cannot be sufficiently reduced and characteristics as a slag product (water absorption rate, etc.) are deteriorated, and the amount of valuable metals such as P ₂ O ₅ is also reduced. Moreover, when the concentration of Al ₂ O ₃ becomes too high, the carbon content remaining in the steelmaking slag after the reforming reduction treatment among the carbon content in the reducing carbon source added during the reforming reduction treatment. In many cases, the separation between the carbon and slag is incomplete, which causes a problem that the strength of the slag after the treatment is reduced.

Therefore, the present inventors conducted the following experiment in order to examine an appropriate addition amount of the Al ₂ O ₃ -containing substance. In this experiment, the relationship between the Al ₂ O ₃ concentration (mass%) in the steelmaking slag during the reforming reduction treatment and the reduction rate of iron oxide (FeO), and the Al ₂ in the steelmaking slag during the reforming reduction treatment. The relationship between the O ₃ concentration (mass%) and the compressive strength (N / mm ² ) of the steelmaking slag after the reforming reduction treatment was investigated.

1) Evaluation of FeO reduction rate After melting 15 kg of hot metal in an induction melting furnace, 2 kg of hot metal pretreatment slag was added, and the change with time in the amount of FeO was investigated. In this experiment, the carbon source for reduction was not added, and the reduction rate by C (carbon content) in the hot metal was evaluated. In this experiment, the heat supply into the melting furnace was performed by induction heating, and the treatment temperature was kept constant at 1450 ° C. Further, stirring was performed by blowing Ar gas into the bath.

The hot metal pretreatment slag used in this experiment has a basicity (= CaO / SiO ₂ ) of 1.2, an MgO concentration of 6% by mass, an FeO concentration of 15% by mass, and an Al ₂ O ₃ concentration of 2 only. The mass was changed from mass% to 42 mass%.

After the hot metal pretreatment slag was added, slag was sampled at an interval of 2 minutes and analyzed. The relationship between the FeO concentration and the treatment time t could be arranged by a primary reaction as shown in the following equation.
−d [FeO] / dt = k · t

Here, k is a reaction rate constant. Further, the reaction rate constant of the reduction reaction of FeO when the Al ₂ O ₃ concentration was 7% by mass to 20% by mass was almost constant. Therefore, the reduction rate was evaluated when the value of the reaction rate constant was less than 7% and more than 20%.

2) Evaluation of compressive strength 5 to 10 mm of coal ash 2t used as a SiO ₂ -containing modifier, 5 to 20 mm used as an Al ₂ O ₃ -containing substance, in a converter reactor holding 100 t of seed hot metal Alumina-based refractory scraps crushed to a diameter and coke 3.3 t having a diameter of 10 to 50 mm used as a carbon source for reduction were charged in advance. Thereafter, the hot metal pretreatment slag 20t was charged into the converter reactor in a molten state. The amount of coal ash to be charged is obtained by collecting hot metal pretreatment slag before charging into a converter reactor, analyzing the composition with a fluorescent X-ray analyzer, and setting a target CaO / SiO ₂ ratio of 1 It was determined by calculating the amount of SiO ₂ required to obtain. Alumina-based refractory waste is a variable because it changes the concentration of Al ₂ O _{3 in} the slag after the reforming reduction treatment. The Al ₂ O ₃ concentration after the reforming reduction treatment was changed from 5% by mass to 42% by mass.

  Moreover, coke was made into the addition amount which becomes 15 mass% in an external number with respect to 100 mass% of the hot metal pretreatment slag with which the carbon content was charged to the converter reactor.

After charging the slag, oxygen was supplied from the top blowing lance, and the melt reforming reduction treatment was performed for 18 minutes. The treatment temperature was 1400 ° C. to 1470 ° C., and the slag during the treatment was always kept in a molten state. In addition, 10-50 mm diameter coke was continuously supplied from the upper side of the reaction vessel during the melt reforming reduction treatment in order to supplement the carbon consumed by the combustion with the top blown oxygen and the reduction of the iron oxide in the slag. . Regarding the coke supply rate at this time, the amount Q (Nm ³ / h) of exhaust gas generated by the melt reforming reduction treatment and the CO concentration and CO ₂ concentration (volume%) in the exhaust gas were continuously measured. Based on the value, it was determined from the following equation.
Coke supply speed (kg / h)
_{= (% CO +% CO 2} ) /100×Q/22.4×12/ ( carbon ratio in the coke)
(“% CO” and “% CO ₂ ” represent the CO concentration and CO ₂ concentration (volume%) in the exhaust gas, respectively.)

  After completion of the melt reforming reduction treatment, the treated reforming slag was discharged into a slag pan and solidified.

Here, as an analysis method of the slag composition in this experiment, fluorescent X-ray analysis was performed in accordance with JIS K 0119. Further, as the reduction rate of FeO, a reduction rate index, which is a relative value of the reduction rate when the reduction rate of FeO when the Al ₂ O ₃ concentration is 7% by mass to 20% by mass, is used. Furthermore, the compressive strength of the steelmaking slag after the reforming reduction treatment was measured in accordance with JIS A1132. The measurement results are shown in Table 2 and Table 3 below.

As a result of this experiment, the relationship between the Al ₂ O ₃ concentration (mass%) in the steelmaking slag during the reforming reduction treatment and the reduction rate of iron oxide (FeO) is as shown in FIG. ₃ shows that the relationship between the Al ₂ O ₃ concentration (mass%) in the steelmaking slag during the treatment and the compressive strength (N / mm ² ) of the steelmaking slag after the reforming reduction treatment is as shown in FIG. It was. FIG. 2 is a graph showing an example of the relationship between the Al ₂ O ₃ concentration (% by mass) in the steelmaking slag during the reforming reduction treatment and the reduction rate of iron oxide (FeO). FIG. 3 is a graph showing an example of the relationship between the Al ₂ O ₃ concentration (mass%) in the steelmaking slag during the reforming reduction treatment and the compressive strength (N / mm ² ) of the steelmaking slag after the reforming reduction treatment. is there.

First, as shown in FIG. 2, with respect to the reduction rate of FeO, as the Al ₂ O ₃ concentration in the steelmaking slag during the reforming reduction treatment increases, the reduction rate of FeO also increases, and the reforming reduction treatment The reduction rate of FeO is constant when the Al ₂ O ₃ concentration in the steelmaking slag is 7 mass% or more and 20 mass% or less, and the Al ₂ O ₃ concentration in the steelmaking slag during the reforming reduction treatment is 20 mass%. It has been found that the reduction rate of FeO tends to decrease when the amount exceeds.

The relationship between the Al ₂ O ₃ concentration in the steelmaking slag during the reforming reduction treatment and the reduction rate of FeO shows the above-mentioned tendency because the Al ₂ O ₃ concentration is in the range of 7% by mass to 20% by mass. Is considered to be because the viscosity of the slag is sufficiently lowered and the reduction reaction of FeO is promoted. More specifically, as described above, when the seed hot metal is used, the reaction site of the steelmaking slag reduction reaction is mainly the hot metal / slag interface, but when the viscosity of the slag is high, the slag Movement to the hot metal / slag interface, which is a high reduction reaction site of FeO, is prevented. Accordingly, when the Al ₂ O ₃ concentration is in the range of 7% by mass or more and 20% by mass or less and the viscosity of the slag is sufficiently low, the FeO in the slag reaches the reaction site faster, so the reduction of the FeO Speed will also increase. Here, the reduction rate of only FeO is seen, but the same can be said for other oxides such as P ₂ O ₅ .

Further, as shown in FIG. 3, the compressive strength of the steelmaking slag after the reforming and reducing treatment increases as the Al ₂ O ₃ concentration in the steelmaking slag during the reforming and reducing treatment increases. , the concentration of Al ₂ O ₃ is compressed in a range of 20 wt% or less 7 mass% or more intensity in steelmaking slag in the reforming reduction treatment is constant, the Al ₂ O ₃ concentration in the steelmaking slag in the reforming reduction treatment When it exceeded 20 mass%, it turned out that it exists in the tendency for compressive strength to fall.

The relationship between the Al ₂ O ₃ concentration in the steelmaking slag during the reforming and reduction treatment and the compressive strength of the slag after the treatment shows the above-described tendency because the Al ₂ O ₃ concentration is 7% by mass or more and 20% by mass. In the following range, since the viscosity of the slag is sufficiently low, the carbon content remaining in the steelmaking slag after the reforming reduction treatment out of the carbon content in the reducing carbon source added during the reforming reduction treatment It is thought that this is because the carbon content can be separated from the slag.

It should be noted that the reduction rate of FeO and the compressive strength of steelmaking slag are constant when the Al ₂ O ₃ concentration is in the range of 7% by mass or more and 20% by mass or less. The slag viscosity is constant in this concentration range. Because.

  Moreover, the separation of the carbon content in the steelmaking slag and the slag is usually carried out by floating the carbon content in the modified slag after the treatment in the molten state. At this time, if the viscosity of the modified slag after the treatment is high, the floating of the carbon content is hindered, so that the separation of the carbon content and the slag as the reducing agent may be incomplete. In addition, if there is a large amount of carbon remaining in the modified slag after treatment, it takes time to float, so the viscosity of the slag rises due to the temperature drop during that time, and separation of the carbon and slag as the reducing agent May be incomplete.

Thus, when the Al ₂ O ₃ concentration in the steelmaking slag during the reforming reduction treatment is less than 7% by mass, the viscosity of the slag is high, and the reduction of oxides such as iron oxide and P ₂ O ₅ in the slag is performed. Since the speed becomes slow, the time required for the reforming and reducing process becomes long, and the production efficiency decreases. On the other hand, when the Al ₂ O ₃ concentration in the steelmaking slag during the reforming reduction treatment exceeds 20% by mass, the viscosity of the slag once lowered is increased again, and oxides such as iron oxide and P ₂ O ₅ in the slag Since the reduction rate of is slowed down, the time required for the reforming reduction treatment becomes longer and the production efficiency is lowered. In addition, when the Al ₂ O ₃ concentration in the steelmaking slag during the reforming reduction treatment exceeds 20% by mass, carbon added as a reducing agent tends to remain in the steelmaking slag after the reforming reduction treatment. , The strength of the modified slag after processing is reduced.

Therefore, in the steelmaking slag treatment method according to the present invention, the steelmaking slag is improved in the reduction rate such as FeO in the steelmaking slag during the reforming reduction treatment, and is refined and high in strength by the reforming reduction treatment. In order to obtain slag, it was decided to add the Al ₂ O ₃ -containing material so that the Al ₂ O ₃ concentration in the steelmaking slag was 7% by mass or more and 20% by mass or less throughout the reforming and reducing treatment. In order to more reliably achieve the effect of improving the reduction rate of FeO or the like and the effect of improving the strength of the reformed slag, the lower limit of the amount of the Al ₂ O ₃ -containing substance is not improved. Through addition, it is preferable to add so that the Al ₂ O ₃ concentration in the steelmaking slag is 8% by mass or more, and it is more preferable to add it to be 10% by mass or more. On the other hand, with respect to the upper limit of the addition amount of the Al ₂ O ₃ -containing substance, from the viewpoint of reducing costs while maintaining the effect of improving the reduction rate of FeO and the like and the effect of improving the strength of the modified slag, Throughout the treatment, it is preferably added so that the Al ₂ O ₃ concentration in the steelmaking slag is 19% by mass or less, and more preferably 18% by mass or less.

In the case of using coal ash as the SiO ₂ content modifier, since the Al ₂ O ₃ is contained in the coal ash, considering the amount of coal ash was added as a SiO ₂ content modifier That is, it is necessary to subtract the amount of Al ₂ O ₃ contained in the coal ash added as the SiO ₂ -containing modifier and determine the amount of the Al ₂ O ₃ -containing material to be added.

Incidentally, at the initial stage of addition of the Al ₂ O ₃ containing substance, a time when the Al ₂ O ₃ concentration in the steelmaking slag does not reach 7% by mass or more and 20% by mass or less inevitably occurs, but such a time is short. the time, if this degree, it can be assumed that throughout the reforming reduction treatment, was added 20 wt% or less 7 mass% or more Al ₂ O ₃ containing materials.

(Reduction carbon source and combustion carbon)
In the present invention, as a reducing carbon source and a combustion carbon source used for the reduction treatment as described above, coke can be mainly used, but is not limited thereto, for example, waste plastic, Carbonaceous waste such as biomass and pulp waste can also be used. Such carbonaceous waste may be used as either a reducing carbon source or a burning carbon source, or may be used as both a reducing carbon source and a burning carbon source.

[Reformed slag according to the present invention]
Although the steel slag treatment method according to the present invention has been described in detail above, the modified slag according to the present invention obtained by the above-described reforming reduction process will be described in detail.

The reformed slag according to the present invention is obtained by adding a SiO ₂ -containing reforming material and a reducing carbon source to the steelmaking slag while heating the steelmaking slag with a heating means, and subjecting the steelmaking slag to a melt reforming reduction treatment. In addition, the composition in the obtained slag satisfies at least the following conditions (i) and (ii).
(I) Al ₂ O ₃ concentration is 7% by mass or more and 20% by mass or less (ii) Basicity is 0.7 or more

First, the type of steelmaking slag, the heating means, the SiO ₂ -containing reforming material, the reducing carbon source, and the like are as described above, and thus detailed description thereof is omitted here.

(Composition of modified slag)
<About Al ₂ O ₃ concentration>
As for the condition (i), when the Al ₂ O ₃ concentration is less than 7% by mass, the viscosity of the slag is high, and the reduction rate of oxides such as iron oxide and P ₂ O ₅ in the slag is slow. For this reason, the time required for the reforming reduction treatment becomes longer, and the production efficiency is lowered. Therefore, the Al ₂ O ₃ concentration is set to 7% by mass or more. On the other hand, when the Al ₂ O ₃ concentration exceeds 20% by mass, the viscosity of the slag once lowered is increased again, and the reduction rate of oxides such as iron oxide and P ₂ O ₅ in the slag is decreased. The time required for the quality reduction treatment becomes longer, the production efficiency decreases, and the carbon added as a reducing agent tends to remain in the steelmaking slag after the reforming reduction treatment. In order to decrease, the Al ₂ O ₃ concentration was set to 20% by mass or less. Further, Al ₂ O ₃ for the concentration of the lower limit value, in order to achieve the effect of improving the strength of the effect of improving and reforming slag reduction rate, such as FeO and more reliably, Al ₂ O ₃ in the reformed slag The concentration is preferably 8% by mass or more, and more preferably 10% by mass or more. On the other hand, the upper limit of the concentration of Al ₂ O _3, while maintaining the effect of improving the strength of the effect and modifying slag reduction rate, such as FeO, from the viewpoint of reducing the more cost, in the reformed slag Al ₂ The O ₃ concentration is preferably 19% by mass or less, and more preferably 18% by mass or less.

<About basicity>
In addition, with regard to the above condition (ii), the modified slag has a strength that can be sufficiently used for high-grade applications such as upper-layer roadbed materials, aggregates for concrete, stone raw materials (such as cracked stones), and abrasive sands. The basicity of the modified slag was defined as 0.7 or more.

The critical values of the Al ₂ O ₃ concentration and the basicity are defined based on the results of the above-described experiment, and detailed description thereof is omitted here.

<About S concentration>
Further, as the composition of the modified slag according to the present invention, the S concentration in the modified slag is preferably 0.7% by mass or less, more preferably 0.6% by mass or less, More preferably, it is at most mass%. Thus, the composition in which the S concentration in the reformed slag is 0.7% by mass or less uses oxygen as a heating means in the melt reforming reduction process for obtaining the reformed slag according to the present invention. This can be realized by using a heating means.

Here, depending on the conditions of the above-described reforming and reducing treatment, the composition of the reforming slag according to the present invention can be made similar to the composition of the blast furnace slag generated in the blast furnace. By the way, blast furnace slag has high commercial value because it can be used for high-grade applications such as cement raw materials in terms of appearance, composition, physical properties and the like. However, since the blast furnace slag contains about 1 mass% of sulfur (S) in the slag as shown in Table 4 below, the blast furnace slag has a problem that so-called yellow water is generated. That is, yellow water is yellow elution water in which calcium polysulfide CaS _x generated in the process in which CaS in blast furnace slow cooling slag is oxidized to change into stable CaSO ₄ is dissolved in water, and blast furnace slow cooling slag is Therefore, it is necessary to sufficiently perform an aging treatment before shipping as a product so that yellow water is not generated.

On the other hand, when the reformed slag according to the present invention is obtained by reforming and reducing treatment using heating means using oxygen, as shown in Table 4 above, with the composition can be a composition similar to the blast furnace slag, because the S in the slag is removed from the slag as an exhaust gas becomes oxidized SO _x by oxygen from the heating means, the S concentration in the slag The S concentration in the reformed slag can be reduced to 0.7% by mass or less. Thus, when the S concentration in the slag is low, yellow water is not generated. Therefore, the modified slag according to the present invention can have a composition similar to that of the blast furnace slag, and thus can be used for high-grade applications such as cement raw materials. The aging process required for the slag is also unnecessary. The exhaust gas containing SO _x is subjected to treatment using a generally known exhaust gas desulfurization facility, neutralization by washing with alkaline water, or the like.

<T. About Fe Concentration>
In addition, the composition of the modified slag according to the present invention includes T.I. The Fe concentration is preferably 1% by mass or less, and more preferably 0.5% by mass or less. Here, “T.Fe concentration” means the total concentration of FeO, Fe ₂ O ₃ and metallic iron contained in the slag. T. T. et al. By controlling the Fe concentration to 1% by mass or less, as described above, it is possible to suppress the generation of bubbles mainly composed of CO gas, whiten or transparentize the slag, and increase the added value of the slag. The effect is obtained.

<About MgO concentration>
In addition, as the composition of the modified slag according to the present invention, the MgO concentration in the modified slag is preferably 15% by mass or less. This is because if the MgO concentration is too high, there is a concern about the influence of the volume expansion of MgO (such as generation of minute cracks and open pores).

  Hereinafter, the present invention will be described more specifically with reference to examples. In the following examples, based on the embodiment of the present invention described above, the steelmaking slag is reformed and reduced, and the components and physical properties (water absorption rate and compressive strength) of the treated slag (modified slag). Is evaluated.

Example 1
A converter-type reaction vessel for holding a Taneyu molten iron 100 t, alumina ground to 5~20mm diameter using coal ash 2t of 5~10mm diameter to be used as the SiO ₂ content modifier, as _Al 2 _{O 3} containing materials Refractory waste 2t and coke 3.3t having a diameter of 10 to 50 mm used as a carbon source for reduction were charged in advance. Thereafter, the hot metal pretreatment slag 20t was charged into the converter reactor in a molten state. The amount of coal ash and the amount of alumina refractory debris that were collected were collected from the hot metal pretreatment slag before being charged into the converter reactor, analyzed for the composition with a fluorescent X-ray analyzer, The ratio was determined by calculating the amount of SiO _{2 and the} amount of Al ₂ O ₃ required to obtain a CaO / SiO ₂ ratio of 1.2 and an Al ₂ O ₃ concentration of 15% by mass. Moreover, coke was made into the addition amount which becomes 15 mass% in an external number with respect to 100 mass% of the hot metal pretreatment slag with which the carbon content was charged to the converter reactor.

After charging the slag, oxygen was supplied from the top blowing lance, and the melt reforming reduction treatment was performed for 18 minutes. The treatment temperature was 1400 ° C. to 1470 ° C., and the slag during the treatment was always kept in a molten state. In addition, 10-50 mm diameter coke was continuously supplied from the upper side of the reaction vessel during the melt reforming reduction treatment in order to supplement the carbon consumed by the combustion with the top blown oxygen and the reduction of the iron oxide in the slag. . Regarding the coke supply rate at this time, the amount Q (Nm ³ / h) of exhaust gas generated by the melt reforming reduction treatment and the CO concentration and CO ₂ concentration (volume%) in the exhaust gas were continuously measured. Based on the value, it was determined from the following equation.
Coke supply speed (kg / h)
_{= (% CO +% CO 2} ) /100×Q/22.4×12/ ( carbon ratio in the coke)
(“% CO” and “% CO ₂ ” represent the CO concentration and CO ₂ concentration (volume%) in the exhaust gas, respectively.)

  After completion of the melt reforming reduction treatment, the treated reforming slag was discharged into a slag pan, and the hot metal remained in the converter reactor. Here, at the time of slag discharge, coke added as a reducing carbon source is also discharged at the same time, but because the viscosity of the slag was low, the separability between the coke and slag is good, and the coke is caught in the slag. Without floating on the slag layer. After cooling, when the slag and coke in the converter reactor are removed from the slag pan, the slag and coke can be completely separated, and the coke should be used as a carbon source for reduction in the melt reforming reduction treatment of the next charge. I was able to.

  The components of the slag before and after the reforming reduction treatment, the coal ash used in this example, the alumina refractory waste, and the coke are shown in Tables 5 to 8 below. In addition, as an analysis method of a slag composition in a present Example and Comparative Examples 1-2 demonstrated below, a fluorescent X ray analysis (JISK0119) is used for f * CaO analysis, and the ethylene glycol extraction method ICP emission spectroscopic analysis is used. Using. However, in the analysis of f · CaO, there is a TBP (tribromophenol) method or the like as a method for extracting f · CaO, and any method may be used as long as the extraction can be performed correctly.

In addition, T. Fe is the total concentration of FeO, Fe ₂ O ₃ and metallic iron. FeO, Fe ₂ O ₃ and metallic iron can be evaluated independently using chemical analysis, but when fluorescent X-ray analysis is used as in this example, Can only be analyzed as the total concentration of all components including Fe. In Table 5 below, f · CaO cannot be analyzed by fluorescent X-ray analysis, but is a value analyzed separately as described above. The amount of CaO is shown as an external number.

  As shown in Table 5 above, the reformed slag after the melt reforming reduction treatment has f · CaO that causes volume expansion reduced to less than 1% by mass, which is useful for high-grade applications such as upper roadbed materials. It was improved to a level where there was no problem even if it was changed. In addition, the T.V. in the reformed slag after the melt reforming reduction treatment. As a result of Fe being reduced to less than 0.5% by mass, the slag after cooling was whitened, and even when mixed with ordinary Portland cement and white cement, no difference in appearance was observed.

Moreover, since coke did not remain in the obtained modified slag after the melt reforming reduction treatment, the water absorption was as low as 0.6% by mass, the compressive strength was as high as 62 N / mm ² , sand, bone It was of a quality that could be used as a wood, cracked stone, etc. In addition, in a present Example and Comparative Examples 1-2 demonstrated below, the water absorption was measured based on JISA1109 and JISA1135, and the compressive strength was measured based on JISA1132.

  Furthermore, since the sulfur concentration in the reformed slag after the melt reforming reduction process was as low as 0.1% by mass, yellow water was not generated, and aging treatment was not necessary when used as a substitute for blast furnace slag. It was.

Further, in the reformed slag after the melt reforming reduction treatment, oxides of valuable components such as MnO and P ₂ O ₅ are also reduced to reduce the concentration in the slag, and the valuable components (manganese, Recovered as phosphorus). As a result, as shown in Table 9 below, the concentrations of manganese and phosphorus in the seed bath hot metal increased.

Furthermore, using the same seed hot metal, the melt reforming reduction process was repeated four times, and the valuable components (Mn, P) were recovered. As a result, the concentrations of Mn and P in the seed hot metal are shown in Table 10 below. The concentration shown can be increased. Thereafter, dephosphorization was performed, and a high concentration phosphorus component was efficiently recovered as P ₂ O ₅ in the dephosphorization slag.

(Comparative Example 1)
A converter-type reaction vessel for holding a Taneyu molten iron 100 t, alumina ground to 5~20mm diameter using coal ash 2t of 5~10mm diameter to be used as the SiO ₂ content modifier, as _Al 2 _{O 3} containing materials 5.1t of refractory waste and 3.3t of coke having a diameter of 10 to 50mm used as a carbon source for reduction were charged in advance. Thereafter, the hot metal pretreatment slag 20t was charged into the converter reactor in a molten state. The amount of coal ash and the amount of alumina refractory debris that were collected were collected from the hot metal pretreatment slag before being charged into the converter reactor, analyzed for the composition with a fluorescent X-ray analyzer, The ratio was determined by calculating the amount of SiO _{2 and the} amount of Al ₂ O ₃ required to obtain a CaO / SiO ₂ ratio of 1.2 and an Al ₂ O ₃ concentration of 25% by mass. The coke was added in an amount of 15% by mass based on the mass of 100% by mass of the hot metal pretreatment slag charged in the converter reactor with carbon.

  After charging the slag, oxygen was supplied from the top blowing lance, and the melt reforming reduction treatment was performed for 18 minutes. The treatment temperature was 1400 ° C. to 1470 ° C., and the slag during the treatment was always kept in a molten state. In addition, 10-50 mm diameter coke was continuously supplied from the upper side of the reaction vessel during the melt reforming reduction treatment in order to supplement the carbon consumed by the combustion with the top blown oxygen and the reduction of the iron oxide in the slag. . The coke supply rate at this time was determined by the same method as in Example 1.

After completion of the melt reforming reduction treatment, the treated reforming slag was discharged into a slag pan, and the hot metal remained in the converter reactor. Here, at the time of slag discharge, coke added as a carbon source for reduction is also discharged at the same time. However, since the Al ₂ O ₃ concentration in the modified slag after treatment was as high as 25% by mass, the viscosity of the slag increased. As a result, the separability between coke and slag was poor. Therefore, a large number of coke grains that could not be floated and separated were present inside the modified slag after cooling.

  The slag components before and after the reforming reduction treatment are shown in Table 11 below. Moreover, in this comparative example, the thing shown in the said Tables 6-8 was used similarly to the said Example about coal ash, an alumina-type refractory waste, and coke.

In addition, T. Fe is the total concentration of FeO, Fe ₂ O ₃ and metallic iron. FeO, Fe ₂ O ₃ and metallic iron can be evaluated independently using chemical analysis, but when fluorescent X-ray analysis is used as in this example, Can only be analyzed as the total concentration of all components including Fe. In Table 11 below, f · CaO cannot be analyzed by fluorescent X-ray analysis, but is a value analyzed separately as described above. The amount of CaO is shown as an external number.

  As shown in Table 11 above, the modified slag after the melt reforming reduction treatment has f · CaO that causes volume expansion reduced to less than 1% by mass, and is useful for high-grade applications such as upper roadbed materials. It was improved to a level where there was no problem even if it was changed. However, the T.V. in the reformed slag after the melt reforming reduction treatment. Fe was as high as 2.5% by mass, the slag was not whitened, and could not be used for ordinary Portland cement and white cement raw materials.

Moreover, in the obtained modified slag after the melt reforming reduction treatment, a large amount of coke remained, so that the water absorption was as high as 5.2% by mass, and the compressive strength was as low as 5 N / mm ² . It could not be used as concrete aggregate or ascon aggregate.

Further, in the reformed slag after the melt reforming reduction treatment, oxides of valuable components such as MnO and P ₂ O ₅ are hardly reduced, and valuable components (manganese, It was not possible to sufficiently recover it as phosphorus).

(Comparative Example 2)
A converter-type reaction vessel for holding a Taneyu molten iron 100 t, alumina ground to 5~20mm diameter using coal ash 2t of 5~10mm diameter to be used as the SiO ₂ content modifier, as _Al 2 _{O 3} containing materials Refractory waste 0.3 t, and 10 to 50 mm diameter coke 3.3 t used as a carbon source for reduction were collectively charged in advance. Thereafter, the hot metal pretreatment slag 20t was charged into the converter reactor in a molten state. The amount of coal ash and the amount of alumina refractory debris that were collected were collected from the hot metal pretreatment slag before being charged into the converter reactor, analyzed for the composition with a fluorescent X-ray analyzer, The ratio was determined by calculating the amount of SiO _{2 and the} amount of Al ₂ O ₃ required to obtain a CaO / SiO ₂ ratio of 1.2 and an Al ₂ O ₃ concentration of 6% by mass. The coke was added in an amount of 15% by mass based on the mass of 100% by mass of the hot metal pretreatment slag charged in the converter reactor with carbon.

  After charging the slag, oxygen was supplied from the top blowing lance, and the melt reforming reduction treatment was performed for 18 minutes. The treatment temperature was 1400 ° C. to 1470 ° C., and the slag during the treatment was always kept in a molten state. In addition, 10-50 mm diameter coke was continuously supplied from the upper side of the reaction vessel during the melt reforming reduction treatment in order to supplement the carbon consumed by the combustion with the top blown oxygen and the reduction of the iron oxide in the slag. . The coke supply rate at this time was determined by the same method as in Example 1.

After completion of the melt reforming reduction treatment, the treated reforming slag was discharged into a slag pan, and the hot metal remained in the converter reactor. Here, at the time of slag discharge, coke added as a carbon source for reduction is also discharged at the same time, but since the Al ₂ O ₃ concentration in the modified slag after treatment was low at 6% by mass, the viscosity of the slag increased. As a result, the separability between coke and slag was poor. Therefore, coke grains that could not be floated and separated were present inside the modified slag after cooling.

  The slag components before and after the reforming reduction treatment are shown in Table 13 below. Moreover, in this comparative example, the thing shown in the said Tables 6-8 was used similarly to the said Example about coal ash, an alumina-type refractory waste, and coke.

In addition, T. Fe is the total concentration of FeO, Fe ₂ O ₃ and metallic iron. FeO, Fe ₂ O ₃ and metallic iron can be evaluated independently using chemical analysis, but when fluorescent X-ray analysis is used as in this example, Can only be analyzed as the total concentration of all components including Fe. In Table 13 below, f · CaO cannot be analyzed by fluorescent X-ray analysis, but is a value separately analyzed as described above. The amount of CaO is shown as an external number.

  As shown in Table 13 above, the reformed slag after the melt reforming reduction treatment has f · CaO that causes volume expansion reduced to less than 1% by mass, and is useful for high-grade applications such as upper-layer roadbed materials. It was improved to a level where there was no problem even if it was changed. However, the T.V. in the reformed slag after the melt reforming reduction treatment. Fe was as high as 3.1% by mass and the slag remained black and could not be used as a raw material for ordinary Portland cement and white cement.

Further, since coke remained in the resulting modified slag after the melt reforming reduction treatment, the water absorption was as high as 3.9% by mass, the compressive strength was as low as 6 N / mm ^2, and the concrete bone It could not be used as wood or ascon aggregate.

Further, in the modified slag after the melt reforming reduction treatment, oxides of valuable components such as MnO and P ₂ O ₅ are hardly reduced, and as shown in Table 14 below, valuable components (manganese, It was not possible to sufficiently recover it as phosphorus).

As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

Claims (2)

While the steelmaking slag charged in the reaction vessel holding the hot metal is heated by a heating means using oxygen gas, the SiO ₂ -containing modifier and the reducing carbon source are added to the steelmaking slag, and the steelmaking A modified slag obtained by subjecting a slag to a melt reforming reduction treatment,
Al ₂ O ₃ concentration in the modified slag is 7% by mass or more and 20% by mass or less,
The basicity of the modified slag is 0.7 or more,
The S concentration in the reformed slag Ri der than 0.7 wt%,
The modified slag is characterized in that the total iron concentration in the modified slag is 1% by mass or less . The modified slag according to claim 1 , wherein the MgO concentration in the modified slag is 15 mass% or less.

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