JP2001192721A - Slag generated in steel making stage and treating method for slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make Pb in Pb-containing slag generated in a steel making stage insoluble and also hard to be expanded by hydration. SOLUTION: Slag generated in a steel making stage and containing Pb of 0.001 mass % or more is regulated in such a manner that the basicity of the slag [(T.CaO)/(SiO2)] is controlled to 1.5 or less, and also, the concentration of (MgO) is controlled to 12 mass % or less and is thereafter separated or removed from a bath surface of the molten steel, where (T.CaO) denotes the concentration (mass %) obtained by converting the whole (Ca) contained in the slag into (CaO), (SiO2) denotes the concentration (mass %) of (SiO2) in the slag, and (MgO) denotes the concentration (mass %) of (MgO) in the slag. Since, as for the slag in this invention, the coefficient of vapor expansion satisfies 1.5% or less, and also, the amount of Pb to be eluted from the slag satisfies the environmental standard value, the slag can be utilized as resources.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to slag generated in a steelmaking process, in which the amount of Pb, which is an environmental problem, is reduced to an environmental standard value or less, and slag is used as a resource. The present invention relates to a slag treatment technology for preventing hydration expansion and utilizing slag as a resource such as road materials and building materials.

[0002]

2. Description of the Related Art Generally, a steelmaking process for ordinary steel is a hot metal pretreatment process for removing [Si], [S], [P], etc. in hot metal from a blast furnace. Converter refining process to perform decarburization refining, and finally [C], [S],
It consists of a secondary refining process for removing or adjusting [P], [H], [O], etc., and controls the target composition and composition of molten steel from hot metal.

In the hot metal pretreatment step, a flux containing CaO is injected by a topped car, a ladle, or a converter type furnace, and the treatment is performed by a mechanical stirring method called a KR method. In the converter refining process, processing is performed by an upper-bottom blow converter or a bottom-blower converter, and in the secondary refining process, processing is performed by a vacuum refining facility such as DH or RH or a heat treatment facility such as LF. Is being done.

On the other hand, for stainless steel, high alloy steel, special steel, etc., a melting step of melting raw materials such as scraps and alloys in an electric furnace, and a process of melting the molten molten steel in a top-bottom blow converter, an AOD furnace or a VOD furnace. It is manufactured in a refining process in which refining is performed, and these processes are also called steel making processes.

In the steel making process as described above, [C],
The removal of impurities such as [S] and [P] is carried out.
Oxidation of [Si], [Al], etc. occurs, and oxides, such as (SiO ₂ ) and (Al ₂ O ₃ ), are generated. In addition, as the erosion of the furnace refractories progresses, CaO and MgO are added to prevent erosion of the refractories as much as possible.
Is added. As a result, slag generation is inevitable in the steelmaking process, and the amount of slag generated throughout the entire steelmaking process ranges from about 150 kg to about 250 kg per ton of molten steel. Therefore, in order to efficiently remove impurities using slag, a processing method for controlling the composition and amount of slag has been adopted.

In such a situation, Pb as an impurity is
Other than Pb-containing free-cutting steel, which is intentionally added, is included in raw materials such as scrap or ferroalloys added in blast furnaces and electric furnaces, and in coolants and reducing materials supplied to top-bottom blow converters, AOD furnaces, etc. Have been. Pb is a low-melting, low-boiling metal that is removed as a gas during melting or refining, but remains partially in molten steel and contains (PbO) in slag.
May remain in the form of The Pb concentration in the slag varies depending on the process and the raw material to be used, but from 0.0001 mass% to as high as 0.05 mass%.

Until now, slag generated in the steel making process has been
It has been considered that Pb concentration is extremely low as compared with incineration ash of garbage, and therefore, elution to water does not occur. But,
In recent years, environmental issues have become more important, and the elution characteristics of various components contained in slag into water have been grasped. It has been found that some of them do not satisfy the condition of 0.01 mg / l or less.

[0008] Under such circumstances, there is no disclosure of a treatment method for preventing the elution of Pb from the slag, or a slag composition condition for preventing the elution of Pb. For example, see `` Materials and Processes, vol. 12, (1999), p. 1
Only by adding iron and steel slag to waste incineration ash, as shown in p. 45 and p. 146, to reduce the Pb elution amount of incineration ash to 0.3 mg / l or less, the criterion for industrial waste for disposal. It is. Even this method is a method for preventing elution in a region where the amount of Pb eluted is high, and is of a laboratory scale. On an industrial scale, no Pb elution preventing effect has been proven.

Up to now, slag generated in the steelmaking process, particularly slag generated in the stainless steel smelting and refining process, and slag generated in the secondary refining process of ordinary steel, have been landfilled for a long time. . In recent years, from the viewpoint of depletion of landfill sites and effective use of slag as resources, for example, use as roadbed materials and building base materials has been tested. However, the slag generally promotes solidification (P ₂ O ₅ ), has a low concentration of (Fe ₂ O ₃ ), and promotes hydration expansibility (MgO), (CaO)
Since the concentration is high, powdering and hydration swelling are intense after the waste treatment, and it does not become a stable state even after being left for a long period of time.

Regarding the prevention of slag powdering, for example, as disclosed in JP-A-59-115982, the slag basicity [(T.CaO) / (SiO ₂ )] is set to about 1.5 or less. Or a method using a slag powdering inhibitor as disclosed in JP-A-1-259114. These methods can prevent slag from pulverizing, but have no effect on hydration expansion. In addition,
Powdered slag is added to water and concrete,
Agglomeration can also be performed by hydration agglomeration, and pulverization of slag is not a major problem.

On the other hand, regarding the swelling property by hydration,
It is known that CaO and MgO contained in the slag undergo a hydration reaction and expand to form Ca (OH) ₂ and Mg (OH) ₂ , respectively. No quantitative knowledge on the relationship has been obtained. Therefore, in recent years, the present inventors have disclosed, as shown in JP-A-9-316518 and JP-A-9-316520,
A waste treatment method for making the slag hardly hydrated and expandable slag was presented.

The waste treatment method disclosed in Japanese Patent Application Laid-Open No. 9-316518 is a method for adjusting the slag composition so that the index M represented by the following formulas (1) to (3) becomes 0 or less.
The waste disposal method disclosed in Japanese Patent No. 316520 is a method of adjusting the slag composition so as to satisfy the following expressions (4) and (5). Log α = −2.34 (T.CaO) / (SiO ₂ ) +4.39 (1) D = (SiO ₂ ) / (0.366 α + 0.263) (2) M = (MgO) − [0.123αD + 0.265 (Cr ₂ O ₃ ) +0.395 (Al ₂ O ₃ ) −0.722 (T.Fe)]… (3) However, (T.CaO) converts all (Ca) contained in slag to (CaO) concentrations (mass%), (SiO ₂₎ is in the slag (SiO ₂₎ concentration (ma
ss%), (MgO) is the (MgO) concentration in slag (mass%), (Cr ₂ O
₃ ) is (Cr ₂ O ₃ ) concentration (mass%) in slag, (Al ₂ O ₃ ) is (Al ₂ O ₃ ) concentration (mass%) in slag, and (T.Fe) is slag (TF
e) The concentration (mass%), α, D and M are indices determined from the slag composition. (T.CaO) / (SiO ₂ ) ≦ 1.8… (5) (MgO) ≦ 0.395 (Al ₂ O ₃ ) +0.277 (SiO ₂ )… (6)

The present inventors have conducted a subsequent investigation and found that
Even if the conditions described in JP-316518A and JP-A-9-316520 are satisfied, it has been discovered that some slags exhibit hydration swelling properties, and that the slags must be hardly hydrated. I realized that presentation was becoming necessary. In addition, they also recognized that it is necessary to present conditions for preventing the elution of Pb.

[0014]

DISCLOSURE OF THE INVENTION The present invention relates to a method for producing slag containing Pb in an amount of 0.001 mass% or more in a steelmaking process.
The purpose of the present invention is to present a slag treatment method and conditions for slag that suppress the elution amount of 0.01 mg / l or less, which is the environmental standard value, by insolubilizing Pb without removing Pb, and suppress hydration swelling ( Subject).

[0015]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems. The gist of the present invention is that slag generated in the steel making process and containing Pb of 0.001 mass% or more is converted to slag basicity.
[(T.CaO) / (SiO ₂ )] 1.5 or less and (MgO) concentration 12 mass
% Or less, and then separated or removed from the molten steel bath surface, or Pb generated in the steelmaking process
Slag separated or removed from the bath surface of the molten steel before the adjustment of the slag composition is heated and melted, and then the slag basicity [(T.CaO) / (SiO ₂ )] 1.5 The method for treating slag generated in the steelmaking process, characterized in that Pb is insolubilized and hardly swellable and expandable by adjusting the concentration so as to be not more than and the (MgO) concentration is 12 mass% or less. is there. However, (T.CaO) is the total (C
a) converted to (CaO) (mass%), (SiO ₂ )
(SiO ₂ ) concentration (mass%), (MgO) is the slag (MgO) concentration (mass
s%).

[0016] Further, Pb generated in the steel making process is 0.001 mass%.
After adjusting the slag containing the above so that the slag expansion index I defined by the following formulas (1) to (4) is 3 or less, separating or removing the molten steel from the bath surface, or in the steelmaking process The slag that has been generated and contains 0.001% by mass or more of slag separated or removed from the bath surface of molten steel before the slag composition adjustment is heated and melted, and is defined by the following equations (1) to (4). A method for treating slag generated in a steelmaking process, characterized in that Pb is insolubilized and hardly swellable by adjusting the slag expansion index I to be 3 or less. Log α = −2.34 (T.CaO) / (SiO ₂ ) +4.39 (1) D = (SiO ₂ ) / (0.366 α + 0.263) (2) M = (MgO) − [0.123αD + 0.265 (Cr ₂ O ₃ ) +0.395 (Al ₂ O ₃ ) −0.722 (T.Fe)] (3) I = 0.246 D + M (4) where (T.CaO) is the total amount contained in the slag ( (Ca) is converted to (CaO) (mass%), (SiO ₂ ) is the (SiO ₂ ) concentration in slag (ma
ss%), (MgO) is the (MgO) concentration in slag (mass%), (Cr ₂ O
₃ ) is the (Cr ₂ O ₃ ) concentration (mass%) in the slag, (Al ₂ O ₃ ) is the (Al ₂ O ₃ ) concentration (mass%) in the slag, and (T.Fe) is the slag (TF
e) The concentration (mass%), α, D and M are indices determined from the slag composition.

Further, Pb generated in the steel making process is reduced to 0.001 mass
% Or more, and the slag basicity [(T.CaO) / (Si
O ₂ )] is 1.5 or less and the (MgO) concentration is 12 mass% or less, or the slag expansion index I defined by the above formulas (1) to (4) is 3 or less, and Pb becomes insoluble. And slag generated in the steel making process, which is hardly hydrated and expandable.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Slag generated in a steelmaking process contains (CaO), (MgO), (SiO ₂ ) and (Al ₂ O ₃ ) as main components, and (S) in a de-S process. In the [P] step, (P ₂ O
₅₎ and (FeO), the ordinary steel is decarburization step the (FeO), which is a decarburization step of chromium-containing steel (Cr ₂ O _3), is mainly contained as other components. In addition, (TiO ₂ ), (Na ₂
O), (K ₂ O), (B ₂ O ₃ ) and the like. The basicity is generally used as an index for determining the limit of the slag refining capacity. The basicity is represented by (T.CaO) / (SiO ₂ ) or [(T.CaO) + (MgO)] / [(SiO ₂ ) + (Al ₂ O ₃ )]. S], de [P] and de [O] abilities are improved, and slag has a high refining capacity. However, the higher the slag, the higher the cost and the higher the slag melting point and the lower the reaction rate. Each is controlled to a suitable basicity range. For example, in the steelmaking process of ordinary steel, the hot metal pretreatment process and the converter refining process fall into the range of about 2.5 to 4.5,
In the stainless steel making process, the melting and refining processes are controlled within a range of about 1.2 to 2.0.

In such a high basicity slag, Pb may be present as metal Pb in granular iron, but is generally considered to be present as an oxide as (PbO). Pb concentration in slag generated in steel making process is 0.0001ma
As high as ss%, it is about 0.05mass%, which is extremely lower than the level of several percent in garbage incineration ash. Until now, it was thought that slag generated in the steelmaking process did not elute Pb into water. .

The present inventors have found that even if slag generated in the steel making process contains Pb in an amount of 0.001% by mass or more, the elution amount of Pb does not satisfy the environmental standard value of 0.01 mg / l or less. Discovered to exist. Further, the present inventors have studied variously the differences between the slag in which the Pb elution value exceeds the reference value and the slag in which the Pb does not exceed the reference value, and have found various conditions of the present invention.

The amount of Pb eluted into the aqueous solution depends on the pH of the aqueous solution when the Pb concentration is constant. The amount of Pb eluted increases as the pH increases, that is, as the alkalinity increases. When slag is immersed in water, the higher the basicity of the slag [(T.CaO) / (SiO ₂ )], the greater the amount of CaO in the slag that dissolves in water due to the hydration reaction of the following formula (7). The pH of the aqueous solution after immersion increases. For this reason, it was discovered that in a slag containing a certain amount of Pb or more, Pb elution occurs when the basicity of the slag is high. CaO + H ₂ O = Ca (OH) ₂ … (7)

Further, when the slag is immersed in water at a certain level of slag basicity, the higher the (MgO) concentration in the slag, the more the MgO in the slag dissolves in water by the hydration reaction of the following formula (8). And the pH of the aqueous solution after immersion increases. Therefore, it was discovered that in a slag containing a certain amount of Pb or more, if the basicity of the slag is high and the (MgO) concentration in the slag is high, the Pb elution phenomenon occurs. MgO + H ₂ O = Mg (OH) ₂ … (8)

By elucidating this elution phenomenon, as a condition for suppressing the elution amount of Pb to 0.01 mg / l or less of the environmental standard value, the Pb concentration in slag should be less than 0.001 mass%, or the Pb concentration in slag should be reduced. If the slag basicity is more than 0.001 mass%,
[(T.CaO) / (SiO ₂ )] 1.5 or less and (MgO) concentration 12 mass
% Was derived. If this condition is satisfied, the slag becomes Pb-insoluble slag.

The hydration reaction of CaO and MgO (Eqs. (7) and (8)), which affects the Pb elution phenomenon, greatly affects the swelling swellability of the slag as described above. As a means for evaluating hydration swellability, 10
Leave the slag for 10 days under 0 ° C steam pressurized condition,
A method for measuring the volume expansion coefficient (hereinafter referred to as a vapor expansion coefficient) is standardized. For roadbed materials and building materials, the reference value is 1.5% or less in the coefficient of vapor expansion. The present inventors have investigated the relationship between the slag composition and the coefficient of vapor expansion, and found that the conditions for reducing the amount of Pb eluted below the environmental standard value and the conditions for setting the vapor expansion coefficient to 1.5% or less are completely the same. In other words, slag basicity [(T.CaO) / (SiO ₂ )]
Slags with 1.5 or less and (MgO) concentration of 12 mass% or less
It was found that b was insoluble and hardly swellable.

Further, the present inventors have tried to derive a formula that accurately expresses the slag composition conditions for preventing Pb elution and hydration swelling. As a result of various studies, the following findings were obtained. (a) Among the various mineral phases of slag, the hydration reaction is caused by CaO-SiO ₂ , 2CaO-SiO ₂ , MgO-Al ₂ O ₃ , MgO-Cr ₂ O
₃ , free of mineral phases such as 2CaO-SiO ₂ -MgO
-CaO and free-MgO. (b) As a result of performing various calculations using Thermocalc which is a thermodynamic equilibrium calculation method, the amount of free-CaO in the slag is as described above.
It can be easily obtained by multiplying the index D obtained by the equations (1) and (2) by 0.246. (c) When the amount of free-MgO is determined in the same manner as the amount of free-CaO, the amount can be determined by the index M determined by the above equations (1) to (3). Note that the value of M may be negative in calculation, but in this case, the value of M was set to 0.

From these, the amount of free-CaO in slag and fr
If the sum of the amounts of ee-MgO is defined as a slag expansion index I, the following equation (4) is derived. I = 0.246 D + M (4) As a result of various investigations on the relationship between the slag expansion index I and the Pb elution amount and the vapor expansion rate, the present inventors found that if the slag expansion index I was 3 or less, the Pb elution amount was 0.01 mg. / l or less and satisfying a steam expansion coefficient of 1.5%. That is, fr
If the sum of the amount of ee-CaO and the amount of free-MgO is 3 mass% or less, it means that Pb is insolubilized and becomes a slag that is difficult to hydrate and expand.

The present inventors have confirmed that the processing method of the present invention has the following embodiments. (1) slag in the presence on the bath surface of the molten steel, by adjusting CaO, the added amount of SiO ₂ or Al ₂ O _3, the slag basicity [(T.Ca
O) / (SiO ₂ )] After adjusting the slag composition so as to satisfy 1.5 or less and the (MgO) concentration of 12 mass% or less, the slag is separated or removed from the molten steel bath surface.

(2) With the slag on the bath of molten steel,
Slag basicity [(T.CaO) / (SiO ₂ )] 1.5 or less and (Mg
If you are unable achieve O) concentration 12 mass% or less of the slag composition conditions, after separation or removal of slag from the molten steel, is melted by heating the slag, followed, SiO ₂
Alternatively, Al ₂ O ₃ is added so that the composition of the slag has a slag basicity [(T.CaO) / (SiO ₂ )] of 1.5 or less and a (MgO) concentration of 12
Adjust so as to satisfy mass% or less.

(3) With the slag on the bath of molten steel,
CaO, by adjusting the added amount of SiO ₂ or Al ₂ O _3, wherein
After adjusting the slag composition such that the slag expansion index I defined by the equations (1) to (4) satisfies the condition of 3 or less, the slag is separated or removed from the molten steel bath surface.

(4) With the slag on the molten steel bath surface,
If the slag expansion index I defined by the formulas (1) to (4) cannot achieve the condition of 3 or less, the slag is separated or removed from the molten steel, and then the slag is heated and melted, After that, SiO ₂ or Al ₂ O ₃ was added,
The composition of the slag is adjusted so that the slag expansion index I defined by the equations (1) to (4) satisfies the condition of 3 or less. The choice of methods (1) and (2) and (3) and (4) is optional, but the methods (1) and (2) are simpler and require more detailed control. Selects the method of (3) and (4).

Hereinafter, embodiments of the present invention will be described in detail. The slag treatment of the present invention is applied, for example, to the treatment of slag generated in a steelmaking process as illustrated in FIG. Fig. 1 (a) is a hot metal pretreatment process in a topped car, (b) is a hot metal pretreatment process in a ladle, and (c)
Is the hot metal pretreatment process by the KR method, (d) is the refining process by the top and bottom blown converter, (e) is the secondary refining process by RH,
(F) is a secondary refining process using DH, (g) is a melting process using an electric furnace, (h) is a refining process using an AOD furnace, and (i)
Denotes a refining process using a VOD furnace, wherein 1 denotes a blowing lance, 2 denotes molten steel or hot metal, 3 denotes slag, 4 denotes a stirring blade, 5 denotes a flux charging chute, 6 denotes a bottom blowing tuyere, 7
Denotes a top blowing lance, 8 denotes a gas blowing tuyere, 9 denotes an electrode, 10 denotes a side blowing tuyere, and 11 denotes a bottom blowing porous plug.

In these steps, in order to promote melting or refining efficiently and to protect the refractory of the furnace, it is inevitable to generate slag of 5% or more of the hot metal or molten steel.
Further, since Pb is mixed in from a melting raw material such as scrap or ferromagnetic iron, or a cooling material or a reducing material added in a smelting furnace, Pb is contained in the slag in an amount of 0.0001 to 0.05 ma.
It will be contained in about ss%. 0.00b Pb with this slag
When the content is 1 mass% or more, if the slag is separated or removed from the hot metal or molten steel and cooled and solidified without adjusting the slag composition, slag having a Pb elution value exceeding the environmental standard value is frequently generated.

If the slag is separated or removed from hot metal or molten steel and cooled and solidified in a state of high basicity and high concentration of (MgO) without adjusting the slag composition, The hydration reaction of CaO and MgO results in a slag exhibiting high hydration swelling with a high vapor expansion coefficient.

According to the present invention, the elution amount and vapor expansion coefficient of Pb contained in the slag are determined by comparing free-CaO and free
Focusing on the fact that it increases depending on the sum of the respective amounts of -MgO, slag conditions where free-CaO and free-MgO do not exist, and processing to eliminate free-CaO and free-MgO The purpose of the present invention is to clarify the conditions to achieve the insolubilization of Pb and the swellability of the hydrate.

FIG. 2 shows the relationship between the Pb concentration in slag and the amount of Pb eluted in each step when ordinary steel and SUS304 stainless steel are melted in an electric furnace and refined in an AOD furnace. The Pb concentration was analyzed by a wet chemical analysis method, and the Pb elution analysis was performed in accordance with the analysis method specified by the Environment Agency Notification No. 46.All the values of slag with a Pb elution amount of 0.01 mg / l or less were Pb elution. The amount was 0.01 mg / l.

All the values in the figure are the values of the slag cooled and solidified after separating or removing the slag from the molten steel bath surface, and (T.CaO) / (SiO ₂ ) Value is
1.6 to 2.0, and the slag (MgO) concentration is 12 to 15 mass%. In addition, white circles (hereinafter, sometimes referred to as circles) indicate slag generated in an electric furnace, and white squares (hereinafter, circles).
Sometimes marked with □. ) Indicates slag generated in the AOD furnace.

FIG. 2 shows that the amount of Pb eluted tends to increase with an increase in the Pb concentration in the slag regardless of the slag generation process in the electric furnace and the AOD furnace, satisfying the environmental standard value of 0.01 mg / l or less. It is understood that the Pb concentration in the slag needs to be less than 0.001 mass%. Therefore, the slag to which the present invention is applied is a slag having a Pb concentration in the slag of 0.001 mass% or more.

FIG. 3 shows a process in which ordinary steel and SUS304 stainless steel are melted in an electric furnace and refined in an AOD furnace, and the slag is separated or removed from the molten steel bath surface and then cooled and solidified. Slag immediately after heating, and after heating and melting the slag, SiO ₂ or Al
_In the slag whose slag composition was adjusted by adding ₂ O ₃ , the amount of Pb elution and vapor expansion coefficient in relation to the (T.CaO) / (SiO ₂ ) and (MgO) concentration in the slag were determined. Show.

In the figure, a circle indicates that the amount of Pb eluted was 0.01 mg / l or less,
When the coefficient of vapor expansion is 1.5% or less, the black triangle indicates that the amount of Pb eluted is 0.01 mg / l or less, and when the coefficient of vapor expansion exceeds 1.5%, the black inverted triangle indicates that the amount of Pb eluted is 0.01 mg / l. When the vapor expansion rate exceeds 1.5 / l and the coefficient of vapor expansion is 1.5% or less, a black circle indicates the case where the amount of Pb eluted exceeds 0.01 mg / l and the coefficient of vapor expansion exceeds 1.5%. The Pb concentration in the slag before treatment was
It was 0.001 mass% or more. According to FIG. 3, the condition that both the Pb elution amount and the vapor expansion coefficient satisfy the reference values is that (T.CaO) / (SiO ₂ ) in the slag is 1.5 or less and the (MgO) concentration is 12%.
It turns out that it is below mass%.

FIG. 4 shows a process in which ordinary steel and SUS304 stainless steel are melted in an electric furnace and refined in an AOD furnace. In each step, the slag is separated or removed from the molten steel bath surface and then cooled and solidified. The slag immediately after the slag, and in the slag in which the slag is heated and melted and then SiO ₂ is added and the slag composition is adjusted,
The relation between the slag expansion index I obtained from the equation (4) and the Pb elution amount is shown.

In the figure, the circles indicate the case where the coefficient of vapor expansion is 1.5% or less, and the black circles indicate the case where the coefficient of vapor expansion exceeds 1.5%.
From FIG. 3, it is understood that the condition that both the Pb elution amount and the vapor expansion coefficient satisfy the reference values is a condition in which the slag expansion index is 3 or less. In addition, when comparing FIG. 3 with FIG. 4, those in which the Pb elution amount and the vapor expansion coefficient satisfy the reference values outside the conditions of the present invention are smaller in FIG. It can be seen that the evaluation can be performed with higher accuracy.

As described above, the amount of Pb generated in the steel making process was 0.001 m
After adjusting the slag containing ass% or more so that the composition of the slag satisfies the condition range of the present invention, the slag is separated or removed from the molten steel bath surface, and the slag composition is the condition of the present invention. If the range is not satisfied, the slag is heated and melted, and the slag composition is adjusted so as to satisfy the condition range of the present invention.
Pb elution amount and vapor expansion rate can be obtained. It should be noted that, if the slag satisfies the condition range of the present invention, it is clear that Pb is a slag that is insoluble and hardly swells and expands.

[0043]

[Example] Plain steel or SUS304 stainless steel (8ma
The process of producing molten steel of ss% Ni-18mass% Cr) 60 ton was carried out in the embodiment of the melting step shown in FIG. 1 (g) and the refining step shown in FIG. 1 (h). In the melting process, scrap,
After melting the ferroalloy as a raw material and raising the temperature to a predetermined temperature,
Steel was produced in a ladle with slag. The slag in the ladle is
Before the molten steel was put into the AOD furnace, it was separated into slag pans using a slag pan. In an AOD furnace, coolant is added during refining, and after decarburization refining to a predetermined [C] concentration, in stainless steel, Fe-Si is added as a reducing material to perform reductive refining, and is taken together with slag. Steel was poured into a pan, and the slag was separated into slag pans and removed. For ordinary steel, reduction refining is not performed.
Immediately after the decarburization refining, tapping was carried out on a ladle together with the slag, and after tapping, the slag was separated into slag pans using a waste machine.

Table 1 shows that the composition of the slag is controlled by (T.CaO) / (S
An example in the case of performing at (iO ₂ ) and (MgO) concentrations will be described. The table summarizes the location of slag generation, the type of smelting steel, the slag composition, the presence or absence of slag heat treatment and the slag composition after the treatment, the Pb elution amount and the steam expansion coefficient. Nos. 1 to 8 are invention examples, and Nos. 9 to 16 are comparative examples. Also, No. 1 of the invention example,
No. 3 and No. 6 were separated from the molten steel bath surface after adjusting the slag composition, No. 2, No. 4, No. 5, No. 6, No. 7 and No. 8, This is an example in which the slag is subjected to heat treatment after being separated from the molten steel bath surface to adjust the slag composition.

Table 2 shows an example where the composition of the slag is controlled by the slag expansion index I. The table shows the location of slag, type of smelted steel, Pb concentration in slag, slag expansion index,
The presence / absence of slag heat treatment, the slag expansion index after the treatment, the Pb elution amount and the vapor expansion coefficient are shown together. No. 1
8 is an invention example, and Nos. 9 to 16 are comparative examples. In addition, No. 1, No. 3 and No. 6 of the invention examples were separated from the molten steel bath surface after adjusting the slag composition, No. 2, No. 4, No. 5, No.
No. 6, No. 7 and No. 8 are examples in which slag was heat-treated after separation from the molten steel bath surface to adjust the slag composition.

In the invention example, the slag composition is adjusted when the slag is on the molten steel bath surface, or the slag composition is adjusted after the slag is melted after the slag is melted. By adjusting the slag composition, a slag composition satisfying the condition range of the present invention was obtained. By performing such a treatment, the Pb elution amount and the vapor expansion rate that stably meet the reference values were obtained.

On the other hand, in the comparative example, since the factors affecting the Pb elution amount and the coefficient of vapor expansion were not clarified, the slag composition was not adjusted, and the slag was subjected to heat treatment after separation from the molten steel bath surface. I didn't do that.
Therefore, the Pb elution amount and the vapor expansion coefficient exceed the reference values. The comparative examples satisfying the reference values include the vapor expansion coefficient of No. 9 in Table 1, the elution amount of Pb in No. 16 and the Pb of No. 16 in Table 2.
Only the elution amount was satisfied, and none of them simultaneously satisfied the Pb elution amount and the vapor expansion coefficient.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

According to the method of the present invention, Pb generated in the steel making process
In the slag containing 0.001 mass% or more, the elution amount of Pb is stabilized below the environmental standard value and there is no adverse effect on the environment, and the steam expansion coefficient satisfies 1.5% or less of the standard value. It can be used as a substitute for sand. In addition, it is possible to perform processing to reduce the slag in which the Pb elution amount and the vapor expansion coefficient exceed the reference value to the Pb elution amount and the vapor expansion coefficient that are equal to or less than the reference value, thereby greatly expanding the range in which the slag is used as a resource.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the present invention, in which (a) is a hot metal pretreatment step using a topped car, (b) is a hot metal pretreatment step using a ladle, and (c) is a hot metal pretreatment step using the KR method. Treatment process, (d) is a refining process using a top and bottom blown converter, (e) is a secondary refining process using RH, (f) is a secondary refining process using DH,
(g) is a diagram illustrating a melting process using an electric furnace, (h) is a refining process using an AOD furnace, and (i) is a diagram illustrating a refining process using a VOD furnace.

FIG. 2 is a diagram showing a relationship between Pb concentration in slag and Pb elution amount.

FIG. 3 is a diagram showing positioning of Pb elution amount and vapor expansion coefficient under the relationship between (T.CaO) / (SiO ₂ ) and (MgO) concentration in slag.

FIG. 4 is a diagram showing a relationship between a slag expansion index I and a Pb elution amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Blowing lance 2 ... Molten steel or hot metal 3 ... Slag 4 ... Agitating blade 5 ... Flux charging chute 6 ... Bottom blowing tuyere 7 ... Top blowing lance 8 ... Gas blowing tuyere 9 ... Electrode 10 ... Side blowing tuyere 11 … Bottom blown porous plug

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Masao Igarashi 3434 Shimada, Hikari-shi, Yamaguchi Prefecture Inside Nippon Steel Corporation Hikari Works (72) Inventor Tadanori Matsunami 3434 Shimada, Hikari-shi, Hikari-shi, Yamaguchi New Japan 4K002 AE01 AE02 AE06 BD04 4K013 BA01 CF03 DA03 FA05 FA06

Claims (6)

[Claims] 1. A slag generated in a steelmaking process and containing 0.001% by mass or more of Pb has a slag basicity [(T.CaO) / (SiO ₂ )] of 1.5 or less and a (MgO) concentration of 12% by mass or less. A method for treating slag generated in a steelmaking process, wherein Pb is insolubilized and hardly swellable by separating or removing the molten steel from the bath surface after adjustment as described above. (However, (T.CaO) is the concentration (mass%) of all (Ca) contained in the slag converted to (CaO), and (SiO ₂ ) is the (SiO ₂ ) concentration (mass
%), (MgO) is the (MgO) concentration in slag (mass%). ] 2. The slag before the adjustment of the slag composition which has been generated in the steelmaking process and contains Pb in an amount of 0.001 mass% or more and separated or removed from the molten steel bath surface is heated and melted, and then the slag basicity [( T.CaO) / (SiO ₂ )] 1.5 or less and (MgO)
By adjusting the concentration to be 12 mass% or less, Pb
A method for treating slag generated in a steelmaking process, wherein the slag is made insoluble and hardly swellable. (However, (TC
aO-) concentration converted all contained in slag (Ca) to (CaO) (mass%), (SiO 2) is in the slag (SiO ₂₎ concentration (mass%), (Mg
O) is the slag (MgO) concentration (mass%). ] 3. Slag generated in the steelmaking process and containing 0.001 mass% or more of Pb is adjusted so that the slag expansion index I defined by the following formulas (1) to (4) becomes 3 or less. A method for treating slag generated in a steelmaking process, wherein Pb is insolubilized and hardly swellable by separating or removing it from a bath surface. Log α = −2.34 (T.CaO) / (SiO ₂ ) +4.39 (1) D = (SiO ₂ ) / (0.366 α + 0.263) (2) M = (MgO) − [0.123αD + 0.265 (Cr ₂ O ₃ ) +0.395 (Al ₂ O ₃ ) −0.722 (T.Fe)] (3) I = 0.246 D + M (4) [However, (T.CaO) is the total amount contained in the slag. (Ca) to (CaO)
Concentration (mass%), (SiO ₂ ) is the (SiO ₂ ) concentration in the slag
(mass%), (MgO) is the (MgO) concentration in slag (mass%), (C
(r ₂ O ₃ ) is the (Cr ₂ O ₃ ) concentration (mass%) in the slag, (Al ₂ O ₃ ) is the (Al ₂ O ₃ ) concentration (mass%) in the slag, and (T.Fe) is the slag ( T.
Fe) concentration (mass%), α, D and M are indices determined from the slag composition. ] 4. The slag which has been generated in the steelmaking process and contains 0.001% by mass or more of Pb and which has been separated or removed from the molten steel bath surface before adjusting the slag composition is heated and melted. By adjusting the slag expansion index I defined by the equation (4) to be 3 or less, Pb is insolubilized and hardly swellable. Processing method. Log α = −2.34 (T.CaO) / (SiO ₂ ) +4.39 (1) D = (SiO ₂ ) / (0.366 α + 0.263) (2) M = (MgO) − [0.123αD + 0.265 (Cr ₂ O ₃ ) +0.395 (Al ₂ O ₃ ) −0.722 (T.Fe)] (3) I = 0.246 D + M (4) [However, (T.CaO) is the total amount contained in the slag. (Ca) to (CaO)
Concentration (mass%), (SiO ₂ ) is the (SiO ₂ ) concentration in the slag
(mass%), (MgO) is the (MgO) concentration in slag (mass%), (C
(r ₂ O ₃ ) is the (Cr ₂ O ₃ ) concentration (mass%) in the slag, (Al ₂ O ₃ ) is the (Al ₂ O ₃ ) concentration (mass%) in the slag, and (T.Fe) is the slag ( T.
Fe) concentration (mass%), α, D and M are indices determined from the slag composition. ] 5. A slag which is generated in a steelmaking process and contains 0.001% by mass or more of Pb, and has a slag basicity of [(T.CaO) / (SiO ₂ )].
A slag generated in a steelmaking process, wherein the slag is adjusted to 1.5 or less and (MgO) concentration to 12 mass% or less, insolubilizes Pb, and has a low hydration expandability. (However, (T.CaO)
Is the concentration (m) of the total (Ca) contained in the slag converted to (CaO).
ass%), (SiO ₂₎ is in the slag (SiO ₂₎ concentration (mass%), (MgO)
Is the slag (MgO) concentration (mass%). ] 6. A slag generated in a steel making process and containing Pb of 0.001 mass% or more, wherein a slag expansion index I defined by the following equations (1) to (4) is adjusted to 3 or less, and Pb is insolubilized. A slag generated in a steelmaking process, which is hardly hydrated and expandable. Log α = −2.34 (T.CaO) / (SiO ₂ ) +4.39 (1) D = (SiO ₂ ) / (0.366 α + 0.263) (2) M = (MgO) − [0.123αD + 0.265 (Cr ₂ O ₃ ) +0.395 (Al ₂ O ₃ ) −0.722 (T.Fe)] (3) I = 0.246 D + M (4) [However, (T.CaO) is the total amount contained in the slag. (Ca) to (CaO)
Concentration (mass%), (SiO ₂ ) is the (SiO ₂ ) concentration in the slag
(mass%), (MgO) is the (MgO) concentration in slag (mass%), (C
(r ₂ O ₃ ) is the (Cr ₂ O ₃ ) concentration (mass%) in the slag, (Al ₂ O ₃ ) is the (Al ₂ O ₃ ) concentration (mass%) in the slag, and (T.Fe) is the slag ( T.
Fe) concentration (mass%), α, D and M are indices determined from the slag composition. ]