JP2003226906A - Method of suppressing elution of fluorine in steel making slag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of suppressing the elution of fluorine that from steel making slag of ≥0.5 wt.% fluorine-containing stainless steel, Fe-Ni alloy steel, or a Ni alloy is effectively suppressed by a relatively inexpensive means. <P>SOLUTION: Phosphorous (P) is added to fluorine-containing steel making slag in an amount satisfying the relation in the following inequality of (P wt.%)≥10X; wherein, x=-1.161logä(CaO wt.%)/(SiO<SB>2</SB>wt.%)}+0.492log(F wt.%)-0.991, so that the elution of fluorine from the slag is suppressed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to stainless steel and Fe-
Eliminating the inconvenience that occurs when using steelmaking slag generated when manufacturing Ni alloy steel or Ni-based alloys as a material for civil engineering and construction, that is, suppressing the elution of fluorine from the slag We propose an advantageous method for

[0002]

2. Description of the Related Art Stainless steel, Fe-Ni alloy steel or Ni
As slag generated during refining of base alloys, etc., steelmaking slag (primary smelting slag) generated when melting raw materials such as scrap in an electric furnace or converter, molten steel is deoxidized in an AOD furnace (argon oxygen decarburization furnace). There are AOD reduction stage slag (secondary slag) generated when carbon and deoxygenation, or finish slag generated when desulfurizing molten steel or adjusting components.

An example of an electric furnace will be described below as the steelmaking slag. When melting raw materials such as stainless steel, Fe-Ni alloy steel or Ni-based alloys in an electric furnace, it is common to add Si into the furnace and use the heat of oxidation to supplement the melting power energy. Is. As a result, a large amount of SiO ₂ is generated in the furnace, but since this SiO ₂ also causes melting damage of the furnace wall, a method of diluting by adding CaO or the like is adopted. The calcium silicate-based compound produced by SiO ₂ and CaO is called an electric furnace slag, and the electric furnace slag also contains a small amount of MgO due to melting of the furnace wall.

[0004] Generally, in the operation of an electric furnace, since it is processed at a relatively low temperature, fluorite (main component is Ca
The addition of F ₂ ) is unavoidable, and it is necessary to adjust the melting point and viscosity of the slag to activate the refining reaction and to easily discharge the slag that is no longer needed. For this reason, the electric furnace slag usually contains about 1 to 3 wt% of fluorine.

Regarding the operation of the AOD furnace, especially in the operation during the finishing refining period, in order to activate the refining reaction such as desulfurization of molten steel, (CaOwt%) / (SiO ₂ wt%) is, for example, The slag composition is adjusted to be 1.5 to 3.0. Therefore, since the slag produced during this finishing refining stage has a high melting point, the addition of fluorite (mainly CaF ₂ ) as a slag material lowers the melting point and viscosity of the slag, and the refining reaction such as desulfurization It also makes it easier to discharge unnecessary slag. Therefore, the AOD furnace finishing refining slag also contains about 1 to 6 wt% of fluorine.

[0006] By the way, regarding fluorine, a notification was issued in March 2001 regarding the addition of soil environmental standard items, and the environmental standard was clarified. Up to now, since there is no emission control for fluorine, almost no study has been made on a method for reducing the elution of fluorine contained in slag. Therefore, when using this slag as a substitute for sand or crushed stone for materials for civil engineering and construction, when the slag comes into contact with rainwater or groundwater, the fluorine contained in the material elutes and the soil environment The possibility has arisen that the criteria cannot be met.

Conventionally, as a technique for reducing the elution of fluorine from such a steelmaking slag, JP2000-225383A, JP2000-247694A, JP2000-335946A, or JP2000-336421A. There is a method disclosed in a bulletin or the like. For example, in Japanese Unexamined Patent Publication No. 2000-335946, a fluorine-containing steelmaking slag contains a fluorine-fixing agent (a synthesized calcium aluminate compound, a naturally-occurring calcium aluminate mineral, and / or a calcium aluminate compound. Next refining slag) and a volume increasing material (decooling blast furnace slag, granulated blast furnace slag, concrete scraps and / or limestone) are mixed, and the calcium ion, aluminate ion or hydroxyl ion, etc. eluted from the fluorine fixing agent Captures the fluorine ions eluting in
A method for coprecipitation to remove fluorine is proposed.

Further, in Japanese Patent Laid-Open No. 2000-248307, fluorite which is a main source of fluorine is not used as a slag material,
Instead, a steelmaking method using an aluminum-containing substance is proposed. However, each of these methods has the following problems.

In the former method, a calcium aluminate-based compound or a substance containing a large amount of calcium aluminate compound is used as a fluorine-removing material, so it is necessary to separately procure them. Synthetic products are extremely expensive and are not suitable for using by-products such as steelmaking slag.

Further, the slag generated in the ordinary stainless steel refining process is mainly composed of calcium silicate compounds, and it is practically difficult to make the refining slag containing a large amount of calcium aluminate compound. Even if the calcium aluminate-based compound can be procured from the outside, the method according to the above-mentioned conventional technique can be applied to the steel slag 100 to be treated.
Since a maximum of 80 parts by weight is required with respect to parts by weight, the final amount of by-products is almost double that before treatment. Therefore, the above-mentioned conventional techniques are based on stainless steel, Fe-Ni alloy steel, or Ni.
It is not desirable as a method for converting slag, which is a by-product of base alloys, into a material.

The latter is a method in which an aluminum-containing substance is used instead of fluorite. In this method as well, in the furnace raw material such as main raw material, slag material, recycled raw material, or refractory waste. Since fluorine is contained as an impurity, a maximum of about several thousand ppm inevitably migrates into the slag. In other words, this method is also able to reduce the elution amount of fluorine as compared with the conventional slag containing about 1 to 3 wt% fluorine, but satisfies the environmental standard value of fluorine elution amount of 0.8 mg / l or less. It was insufficient as a measure to make it happen.

Further, it is possible to use an aluminum-containing substance as a slag material at the time of AOD furnace finishing refining of stainless steel, Fe-Ni alloy steel or Ni-base alloy molten steel, but the desulfurization performance of the produced slag. Is deteriorated and harmful non-metallic inclusions are generated, which may adversely affect the product quality, which is not preferable.

In addition, in Japanese Patent Laid-Open No. 2000-226610, during hot metal dephosphorization of ordinary steel, by adjusting the P concentration in the dephosphorization slag, fluorine is fixed as fluoroapatite in the slag, and it is discharged to drainage. We have proposed a hot metal dephosphorization method that suppresses the elution of fluorine. However, with respect to this method, for example, since stainless steel and the like contain chromium, dephosphorization itself becomes difficult, and it becomes difficult to adopt it as a hot metal dephosphorization method.

[0014]

Therefore, in view of the problems of the above-mentioned respective prior arts, the object of the present invention is to provide stainless steel or Fe-Ni containing 0.5 wt% or more of fluorine.
There is a proposal of a method for suppressing the elution of fluorine from a steelmaking slag such as an alloy steel and a Ni-based alloy, which can effectively suppress the elution of fluorine by a relatively inexpensive means.

[0015]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present inventors have developed a fluorine-containing stainless steel or Fe-
To investigate in detail the elution behavior of fluorine from the above refining slag of Ni alloy steel and Ni-based alloys (hereinafter simply referred to as "steel slag"), and find a method for easily and effectively suppressing the elution of fluorine. We have repeated various experiments and studies. As a result, it was found that when phosphorus (P) was added to the slag, the elution of fluorine could be effectively suppressed by a relatively inexpensive means.

The present invention developed on the basis of such findings is characterized in that phosphorus (P) is added to a steelmaking slag containing fluorine to suppress the elution of fluorine from the slag. This is a method for suppressing the elution of fluorine in steelmaking slag.

In addition, in the present invention, steelmaking slag
Phosphorus (P) is added by the following formula; (Pwt%) ≧ 10^x However, x = −1.161og {(CaOwt%) / (SiO₂wt%)} + 0.4921og (Fwt
%)-0.991 The amount added to the steelmaking slag
Synthetic phosphorus-containing compounds, natural phosphorus-containing minerals,
Choose from phosphorus-containing waste and other phosphorus-containing substances
Use at least one of them, and add water to the mixture after adding phosphorus.
Stabilization treatment in the presence of water, stabilization treatment in the presence of water
The reason is that the mixture should be sprayed with warm water at 50 ° C or above
Pickle, sprinkle hot water of 80 ℃ or more, or soak, or
How to apply hot water treatment such as aging with steam
Using, and said steelmaking slag is made of stainless steel, Fe
-Flux generated during the production of Ni alloy steel or Ni-based alloy
Steelmaking slag containing 0.5 wt% or more and 7 wt% or less of silicon
It is preferable.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors have studied various additive elements in order to effectively suppress the elution of fluorine (F) from steelmaking slag. As a result, as shown in FIG. 1, it was found that the addition of phosphorus (P) was effective. That is, FIG. 1 shows the relationship between the phosphorus (P) content in the steelmaking slag and the fluorine (F) elution amount. Here, as the steelmaking slag, stainless steel containing 1 to 4 wt% of fluorine, Fe-
What was generated when refining Ni alloy steel and Ni base alloy in an electric furnace was used. In addition, the fluorine elution test complied with the Environmental Agency Notification No. 46, which is a verification method of soil environmental standards. From this test result, it was found that the elution of fluorine can be effectively suppressed by adding phosphorus (P) to the steelmaking slag.

Furthermore, the inventors have based on these test results.
The environmental standard value of fluorine elution amount of 0.8 mg / l or less.
The conditions to be added were examined. As a result, the target product
Between the chemical composition of steel slag and the required phosphorus (P) wt%
We found that there is such a relationship. That is, the dissolution of fluorine
The amount of phosphorus added to the steelmaking slag that can effectively suppress the discharge is C
aO, SiO₂And in relation to F, the following formula; (Pwt%) ≧ 10^x However, x = -1.161og {(CaOwt%) / (SiO₂wt%)} + 0.4921og (Fwt%)
-0.991 To satisfy the relationship of The numerical value of x above is the seed
An experiment of phosphorus addition was conducted on various steelmaking slags, and the results are shown below.
Confirm the elution suppression effect, and use the environmental standard value for the amount of fluorine elution.
By using multivariate regression analysis, the conditions that satisfy 0.8 mg / l or less
Is the formula that was derived.

Here, F from the steelmaking slag by adding P
The mechanism of elution suppression of
I can think of it. That is, F-containing steelmaking slurry containing P
Glue elutes F ions in water and
And phosphate ions are also eluted at the same time. At this time, water
F ions eluted into the calcium ions and
Coprecipitate with phosphate ions, etc._Five(PO_Four)₃Fixed to (OH, F) shape
Then remove it. This is Ca_Five(PO_Four)₃OH and Ca_Five(P
O_Four)₃F, or Ca, which is a solid solution of these_Five(PO_Four) ₃(OH, F) is
Knowledge that it is extremely stable and sparingly soluble in water
It is based on.

According to the conventional method, for example, the method described in Japanese Patent Laid-Open No. 2000-248307, 2 wt% of F is Ca
_{If 5} (PO ₄ ) ₃ F is to be completely fixed in the slag, stoichiometrically about 10 wt% of P is required. However, in the present invention, from the steelmaking slag, only fluorine eluted in water, coprecipitated with calcium ions and phosphate ions, it is sufficient if it can be fixed in solution as Ca ₅ (PO ₄ ) ₃ (OH, F),
The required amount of P depends on the target slag composition, but may be about 0.05 to 0.5 wt%.

Here, it is natural that the final elution amount of F ions is suppressed to a lower value as the F content in the steelmaking slag is smaller, but as another factor, phosphate ions eluted in water are used. If the amount is large, that is, if the amount of P added to the steelmaking slag is large, the eluted F ions are fixed and removed, so that the amount can be kept low.

Further, the greater the amount of calcium ions eluted in water, that is, the main composition of the steelmaking slag, Ca
The higher the ratio of CaO to O and SiO _2, the more the amount of P added can be suppressed to be relatively low. Therefore, the composition of the steelmaking slag is preferably about 0.6 to 4.0 in terms of CaO wt% / SiO ₂ wt%.

Thus, mainly calciu in the slag
The elution amount of F depends on the amount of mu ions and the amount of P added.
The reason why it can be adjusted is that the elution amount of fluoride ion is [Ca²⁺]^Five・
[PO _Four ^3-]³・ [F^-] And the solubility product represented by
This is because this is a constant value.

As the source of the above-mentioned P to be added, synthetic phosphorus-containing compounds such as apatite and various calcium phosphates and naturally occurring phosphorus-containing minerals such as phosphate ore, and paper sludge, dephosphorized slag and human waste treatment sludge. Although it is possible to use phosphorus-containing waste such as, it is economical to add as little as possible within the range satisfying the above formula.

The present invention is based on fluorine ions eluted in water.
Are simultaneously eluted with calcium ions, phosphate ions and
Co-precipitation with hydroxyl ions in water
a_Five(PO_Four) ₃It is a method of removing as (OH, F) solid solution. P's
The addition method is not particularly limited.
Using a method such as adding to the melt or mixing cold.
Good. However, stainless steel, Fe-Ni alloy steel, and Ni
Without degrading the quality of products such as base alloys,
When considering the effect of uniform distribution of P on the entire
It is advisable to add it in the pot and stir it with a slag stream.
Yes.

The reaction of immobilizing fluorine ions in water as Ca ₅ (PO ₄ ) ₃ (OH, F) is carried out in the elution water during the elution test, and when the slag comes into contact with rainwater or groundwater in the actual use environment. It occurs after elution of fluorine, calcium, and phosphate ions in water. However, when it is necessary to prevent elution itself in advance, it is desirable to carry out a stabilization treatment for stabilizing the mixture of steelmaking slag and P in the presence of water. This converts fluorine into Ca ₅ (PO ₄ ) ₃
This is because elution of fluorine ions themselves from the steelmaking slag can be suppressed by completing the reaction of immobilizing (OH, F) in advance. Such stabilization treatment may be natural aging treatment in the atmosphere or water spraying or immersion treatment at room temperature, but in order to stabilize in a shorter period of time, spraying hot water at 50 ° C or higher or hot water It is preferable that the method is such that the material is immersed in water, sprayed with hot water at 80 ° C. or higher, immersed in hot water, or aged by steam.

[0028]

[Examples] Table 1 shows the results of a fluorine elution test as examples. In addition, the fluorine elution test complied with the Environmental Agency Notification No. 46, which is a verification method of soil environmental standards. The steelmaking slag used in the test had ₂₀ to 60 wt% CaO and 25 to 45 wt% SiO ₂ .
%, A1 ₂ O ₃ is ₂ to 20 wt%, MgO is 5 to 15 wt%, F is 0.5 to 6.0 wt%, and the balance contains inevitable impurities represented by Cr ₂ O ₃ , FeO, MnO, etc., (CaO wt%) / (SiO ₂ wt%) is a steel-making slag of stainless steel, Fe—Ni alloy steel, and Ni-based alloy having 0.5 to 3.3.

[0029]

[Table 1]

The phosphorus material added is about 1.0 wt%
Paper sludge, which is a waste containing P before and after, was used. Examples 1 to 7 are, with respect to the steelmaking slag having the above composition, the results of the execution when P was not added, and the elution amount of F was
In all cases, it exceeded the soil environmental standard value of 0.8 mg / l. Example 8 is, although the addition of P, is an example of the case of adding a smaller amount of P than the method proposed by the present invention, although the elution suppressing effect of fluorine was seen, soil environment The standard value of 0.8 mg / 1 or less could not be cleared.

Examples 9 to 17 are examples in which sufficient P was added to the steelmaking slag according to the method proposed by the present invention, and (CaOwt%) / (SiO ₂ wt%) was 0.5 to Fluorine elution was effectively suppressed in a very wide range of slag compositions with around 3 and F around 0.5 to 6 wt%, and in all cases the soil environmental standard value of 0.8 mg / l or less was cleared. Was there.

[0032]

As described above, according to the method of the present invention, the elution of fluorine from the steelmaking slag containing F generated during the production of stainless steel, Fe-Ni alloy steel or Ni-based alloy is compared. It can be effectively suppressed by an inexpensive method. This enabled the use of steelmaking slag, which is a by-product of stainless steel, Fe-Ni alloy steel, and Ni-based alloys, for civil engineering and building materials.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the phosphorus content in steelmaking slag and the amount of fluorine eluted from the slag.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichi Nagashima             4-2 Kojima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa             Main metallurgical industry Kawasaki factory F-term (reference) 4K012 AA01

Claims (6)

[Claims] 1. A method for suppressing elution of fluorine in a steelmaking slag, which comprises suppressing the elution of fluorine from the slag by adding phosphorus (P) to the steelmaking slag containing fluorine. 2. The addition of phosphorus (P) to the steelmaking slag is performed by the following formula; (Pwt%) ≧ 10 ^x, where x = −1.161og {(CaOwt%) / (SiO ₂ wt%)} + 0.4921og (Fwt
The elution suppressing method according to claim 1, wherein the amount is such that the relationship of (%)-0.991 is satisfied. 3. A phosphorus material added to steelmaking slag,
3. The elution suppressing method according to claim 1, wherein at least one selected from synthetic phosphorus-containing compounds, natural phosphorus-containing minerals, phosphorus-containing wastes, and other phosphorus-containing substances is used. 4. The elution suppressing method according to claim 1, wherein the mixture after addition of phosphorus is subjected to a stabilizing treatment in the presence of water. 5. Stabilization treatment in the presence of water, the mixture is sprayed or immersed in hot water of 50 ℃ or more, hot water of 80 ℃ or more, or immersed, or aging with steam, etc. 5. The method for suppressing elution according to claim 4, wherein the method of performing hot water treatment according to claim 4 is used. 6. The steelmaking slag is made of stainless steel or Fe-Ni.
Occurs when manufacturing alloy steel or Ni-based alloys,
6. The elution suppressing method according to any one of claims 1 to 5, which is a refining slag containing 0.5 wt% or more of fluorine.