JP5322860B2 - Recycled slag generation method and recycled slag - Google Patents

Description

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

  Slag produced when chromium steel such as stainless steel is produced (sometimes referred to as chromium-containing steel slag) is inevitably generated in a refining process such as a raw material melting process or decarburization, reduction of generated oxide, desulfurization, Contains several percent chromium oxide. Depending on the presence of this chromium oxide, when slag is reused for roadbed materials, marine applications, etc., harmful hexavalent chromium may be eluted into water, soil, etc. Making it difficult.

As a method for preventing elution of hexavalent chromium from chromium-containing steel slag, there are methods shown in Patent Documents 1 to 3.
In Patent Document 1, aluminum ash and a magnesia-based substance are spread in a receiving pan, and slag in a molten state is discharged into the receiving pan. In this method, spinel having a composition of MgO.Al ₂ O ₃ is formed and stabilized by solid solution of chromium oxide therein, thereby preventing the oxidation of chromium, that is, the formation of hexavalent chromium.

  Patent Document 2 suppresses hexavalent chromium elution by controlling the slag composition in a molten state in which a uniform state of slag is maintained, and the slag generated in the smelting and refining process of chromium-containing steel is used as a bath surface of the molten steel. When separating or removing from the top, the slag is separated by adjusting the desulfurization distribution ratio (S) / [S], which is the ratio of the (S) concentration in the slag to the [S] concentration in the molten steel so as to satisfy the prescribed formula. Or they are removed.

In Patent Document 3, and that more than 80 wt% of the total chromium in the slag is present as FeO · Cr ₂ O ₃ and / or MnO · Cr ₂ O _3, it 2CaO · SiO ₂ content is less 3 wt%, By controlling the slag composition and the mineral phase in the slag, such as the sum of the iron oxide mass and manganese oxide mass in the slag is 1.5 times the total chromium mass, the elution amount of hexavalent chromium is suppressed. .

In general, chromium-containing steel slag exists as trivalent chromium (Cr ₂ O ₃ ) in a high-temperature molten state, and this trivalent chromium is oxidized by the conditions of the cooling process, thereby hexavalent chromium. Is supposed to be generated. Therefore, after reducing the trivalent chromium (Cr ₂ O ₃₎ concentration led to reduction of chromium by adjustment of Patent Document 4 and Patent Document 5, the slag basicity (CaO / SiO _2), after Haikasu It controls the area where slag is exposed to the atmosphere and prevents oxidation of trivalent chromium.

JP-A-6-171993 Japanese Patent No. 3586311 Japanese Patent Laid-Open No. 2005-298734 JP 2008-50700 A JP 2008-81845 A

As described above, in order to suppress the elution of hexavalent chromium from the chromium-containing steel slag, it is important to control the slag composition and the like. Is very difficult.
In view of the above problems, an object of the present invention is to provide a method for producing recycled slag and a recycled slag capable of reliably suppressing elution of hexavalent chromium when recycling oxidized slag.

In order to achieve the object, the present invention takes the following technical means.
That is, the technical means according to the method of the present invention is a method for producing recycled slag in which oxidized slag produced when smelting and refining chromium-containing steel in an electric furnace is used as a recycling slag. _{: 35~51%, SiO 2: 5~16} %, Al 2 O 3: 0.5~11%, MgO: 3~15%, MnO: 2~11%, CaF 2: 0.1~0.5 %, T.M. Fe: 14 to 29%, Cr ₂ O ₃ : 0.2 to 6.0%, and the balance of oxidized slag with the balance being inevitable impurities is T.P. By adjusting the FeO / Fe ₂ O ₃ in the Fe content to be 1.25 or more, the oxidized slag is made into a slag for recycling.

The technical means by the thing of this invention is the slag for recycling produced | generated by adjusting the oxidation slag produced | generated when melt-refining chromium-containing steel with an electric furnace , Comprising: By mass%, CaO: 35-51 _{%, SiO 2: 5~16%,} Al 2 O 3: 0.5~11%, MgO: 3~15%, MnO: 2~11%, CaF 2: 0.1~0.5%, T. Fe: 14 to 29%, Cr ₂ O ₃ : 0.2 to 6.0%, the balance being inevitable impurities, and T.I. Lies in that the FeO / _Fe 2 _{O 3} ≧ 1.25 in Fe content.

The inventor focused not on out-of-furnace refining (reduction refining) slag but on oxidized slag generated when oxygen blowing such as converters and electric furnaces.
Generally, when chromium-containing steel is blown in a converter or electric furnace, the concentration of trivalent chromium oxide (Cr ₂ O ₃ ) in the generated slag is higher than that of stainless steel in the AOD method or VOD method. However, when scrap is introduced during refining, Cr contained in the scrap is oxidized, and the concentration of trivalent chromium oxide contained in the oxidized slag is increased.

Depending on the slag composition, the trivalent chromium oxide in the oxidized slag may be further oxidized to produce hexavalent chromium. For this reason, the inventors considered elution of hexavalent chromium even in oxidized slag produced by refining converters, electric furnaces, and the like.
That is, it is important for the inventor to prevent elution of hexavalent chromium when reusing oxidized slag. Hexavalent chromium is changed to hexavalent chromium oxide by partially oxidizing trivalent chromium oxide in the slag. With the recognition that we do, we conducted elite research.

As a result, the inventor has found that the ratio of FeO to Fe ₂ O _{3 in} the slag needs to be 1.25 or more with respect to the composition of the oxidized slag in order to prevent elution of hexavalent chromium.

  According to the present invention, elution of hexavalent chromium from the slag can be reliably suppressed when the oxidized slag is reused.

An example of a refining device for refining chromium steel is shown. This is a summary of the relationship between FeO / Fe ₂ O _{3 in} oxidized slag and the elution amount of hexavalent chromium.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a refining apparatus for refining chromium steel (sometimes referred to as chromium-containing steel) containing Cr such as stainless steel.
As shown in FIG. 1, chromium-containing steel is generally manufactured by melting and refining in an electric furnace 1. The electric furnace 1 melts a cold iron source and the like introduced therein, and refines the melted cold iron source and the like (molten metal 2) and the molten metal 2 directly inserted from the outside, and stores the molten metal 2 A container body 3 to be operated, and a lid 4 covering the container body 3.

The container body 3 and the lid body 4 can be separated vertically. By the container body 3 and the lid body 4, a discharge port 5 is formed on one side (paper surface, right side), and a steel outlet port 6 is formed on the other side (paper surface, left side). In addition, the discharge port 5 and the steel exit 6 may be formed in the container main body 3.
A lance 7 for blowing oxygen or the like into the molten metal in the container body 3 is inserted into the discharge port 5. In addition, the discharge port 5 and the steel exit 6 may be formed in the container main body 3.

The lid 4 and the like are provided with a plurality of electrodes (for example, carbon electrodes) 8 for generating an arc, and the internal cold iron source is melted by arc discharge of the electrodes 8.
In order to manufacture chromium-containing steel using such an electric furnace 1, first, a cold iron source (for example, scrap) is introduced into the container body 3 and auxiliary materials and the like are introduced. Then, by arc discharge by the electrode 8, the cold iron source and the auxiliary raw material are heated and melted to form a molten metal, and oxygen is blown into the molten metal 2 by the lance 7, thereby refining, that is, dephosphorization or decarburization. It is manufactured by doing.

Thus, in the process of producing chromium-containing steel, oxidized slag (slag generated by oxygen blowing) S is generated by refining in the electric furnace 1. The present invention is characterized in that the oxidized slag S generated in the process of producing chromium-containing steel can be reused as a recycled slag without problems for roadbed materials, marine applications and the like.
Hereinafter, the method for producing recycled slag and the recycled slag will be described in detail.

In producing chromium-containing steel, the oxidized slag S produced after refining in the electric furnace 1 or the like is mass%, CaO: 35 to 51%, SiO ₂ : 5 to 16%, Al ₂ O ₃ : 0.5 to 11%, MgO: 3 to 15%, MnO: 2 to 11%, CaF ₂ : 0.1 to 0.5%, T.I. _{Fe: 14~29%, Cr 2 O} 3: contains 0.2 to 6.0%, and the balance is unavoidable impurities. In the slag S oxide, possible inevitable impurities include Na, K, Cl and the like. Although arbitrarily selected for basicity of oxide slag S (CaO / SiO _2), for example, may select a value of 2.5 to 6.0. Further, the title “T.Fe” means “total amount of Fe” contained in the oxidized slag.

When such refined oxidized slag S is simply cooled, the trivalent chromium contained in the oxidized slag S is further oxidized especially during cooling, and a large amount of hexavalent chromium is present when reused for roadbed materials or marine applications. May elute.
As a result of investigating the elution amount of hexavalent chromium from various oxidized slag S containing trivalent chromium (Cr ₂ O ₃ ) by experiments and the like, the elution amount of hexavalent chromium is greatly influenced by the slag composition. It was found that it depends on the presence of iron oxide. That is, according to the present invention, T.O. By adjusting the FeO / Fe ₂ O ₃ in the Fe content to be 1.25 or more, the oxidized slag S can be used as a recycled slag.

Specifically, a reductant (Al, Si, etc.) that reduces Fe ₂ O ₃ is added to the oxidized slag S after refining before the temperature of the oxidized slag S decreases and solidifies. or by iron oxide (FeO) was added (to dilute the Fe ₂ O ₃₎ increasing FeO amount for _{Fe 2 O 3, FeO / Fe} 2 O 3 can be set to 1.25 or more. For example, when the oxidized slag S after refining is discharged, a reducing agent or iron oxide is previously put in a container that receives the discharged oxidized slag S, and then the oxidized slag S is discharged into the container. By making / Fe ₂ O _{3 to} be 1.25 or more and cooling the oxidized slag S, it can be used as a recycled slag.

Next, the reason why elution of hexavalent chromium can be suppressed by setting FeO / Fe ₂ O ₃ to 1.25 or more will be described.
Unlike the out-of-furnace refining slag, the oxidized slag S contains a large amount of molten steel oxidized by oxygen blowing as iron oxide. Generally, the iron content in slag is T.W. Although it is often analyzed as Fe, in practice, divalent iron (FeO) and trivalent iron (Fe ₂ O ₃ ) coexist depending on the oxidation state of slag. This FeO and Fe ₂ O ₃ are affected by the amount of oxygen blowing, for example.

For example, when the ratio of FeO to Fe ₂ O ₃ (hereinafter referred to as FeO / Fe ₂ O ₃ ) is small in the oxidation slag S, the oxygen potential of the oxidation slag S is high, that is, Fe that is an oxidation source during cooling. _Even though it is in a state where there is a large amount of ₂ O _3, it is considered that Cr ₂ O ₃ is more strongly oxidized and, as a result, the amount of hexavalent chromium eluted is increased.
On the other hand, if FeO / Fe ₂ O ₃ is increased and the oxygen potential in the slag is low, that is, if Fe ₂ O ₃ that is an oxidation source during cooling is low, the trivalent chromium becomes hexavalent chromium. It is considered that the oxidation amount of hexavalent chromium is suppressed and the elution amount of hexavalent chromium can be suppressed. That is, if the oxygen potential in the slag is made low by increasing FeO / Fe ₂ O ₃ , the oxidized slag S is unlikely to be in an oxidizing atmosphere even when cooled to make the oxidized slag into recycled slag. It is considered that sometimes trivalent chromium is oxidized and hexavalent chromium is prevented from being generated.

FIG. 2 summarizes the relationship between FeO / Fe ₂ O ₃ and the elution amount of hexavalent chromium by experiments and the like.
As shown in FIG. 2, when FeO / Fe ₂ O ₃ in the oxidized slag S is 1.25 or more, the elution amount of hexavalent chromium can be 0.05 mg / L or less in all experiments. That is, by setting the FeO / Fe ₂ O ₃ in the slag oxide S to 1.25 or more, the elution amount of hexavalent chromium defined by the Environment Agency Notification No. 46 is set to 0.05 mg / L or less. Can do.

As described above, according to the present invention, by mass%, CaO: 35 to 51%, SiO ₂ : 5 to 16%, Al ₂ O ₃ : 0.5 to 11%, MgO: 3 to 15%, MnO: 2 to 2%. 11%, CaF ₂ : 0.1 to 0.5%, T.I. _{Fe: 14~29%, Cr 2 O} 3: contains 0.2 to 6.0%, relative to the balance of inevitable impurities oxide slag S, T. By adjusting the FeO / Fe ₂ O ₃ in the Fe content to be 1.25 or more, a recycled slag having an elution amount of hexavalent chromium of 0.05 mg / L or less can be produced.

Table 1 summarizes examples of recycled slag produced by the method for producing recycled slag of the present invention and comparative examples of recycled slag produced by a method different from the present invention.
The elution amount of hexavalent chromium in Examples and Comparative Examples was measured based on the dissolution test method in accordance with Environment Agency Notification No. 46, which is a test method for soil environment standards. In the examples and comparative examples, the composition of the predetermined oxidation slag S is mixed with a reagent and held in a platinum crucible or a refractory crucible, and the oxidation slag S is formed using an atmospheric firing furnace or an atmospheric firing furnace. It melt | dissolved and solidified the oxidation slag S by subsequent cooling, and obtained the slag sample. The ratio of Fe ²⁺ and Fe ³⁺ was adjusted by mixing predetermined amounts of FeO and Fe ₂ O ₃ reagents.

  In the examples and comparative examples in Table 1, the amount of hexavalent chromium eluted below 0.02 mg / L, which is the analysis limit value, was expressed as “0.00”.

As shown in Comparative Examples 1 to 8, in the oxidized slag (recycled slag), when FeO / Fe ₂ O ₃ is less than 1.25, the elution amount of hexavalent chromium is regarded as an environmental standard. It will exceed 05 mg / L, and the elution amount of hexavalent chromium cannot be suppressed.
On the other hand, as shown in Examples 1 to 8, in the oxidized slag (recycled slag), when FeO / Fe ₂ O ₃ is 1.25 or more, the elution amount of hexavalent chromium is regarded as the environmental standard. 0.05 mg / L or less, and the elution amount of hexavalent chromium can be suppressed.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. In the above embodiment, the oxidation slag generated in the electric furnace when producing chromium-containing steel has been described. However, this oxidation slag may be generated other than outside furnace refining (ladder refining). What is necessary is just to generate | occur | produce in the refining of a converter.

DESCRIPTION OF SYMBOLS 1 Electric furnace 2 Molten metal 3 Container body 4 Lid 5 Exhaust port 6 Steel outlet 7 Lance 8 Electrode

Claims (2)

A method for producing recycled slag, in which oxidized slag produced when melting and refining chromium-containing steel in an electric furnace is made into a slag for recycling,
By _{mass%, CaO: 35~51%, SiO} 2: 5~16%, Al 2 O 3: 0.5~11%, MgO: 3~15%, MnO: 2~11%, CaF 2: 0. 1-0.5%, T.I. Fe: 14 to 29%, Cr ₂ O ₃ : 0.2 to 6.0%, and the balance of oxidized slag with the balance being inevitable impurities is T.P. A method for producing recycled slag, wherein FeO / Fe ₂ O ₃ in the Fe content is adjusted to be 1.25 or more, whereby the oxidized slag is converted into a slag for recycling. Recycling slag produced by adjusting the oxidized slag produced when melting and refining chromium-containing steel in an electric furnace,
By _{mass%, CaO: 35~51%, SiO} 2: 5~16%, Al 2 O 3: 0.5~11%, MgO: 3~15%, MnO: 2~11%, CaF 2: 0. 1-0.5%, T.I. Fe: 14 to 29%, Cr ₂ O ₃ : 0.2 to 6.0%, the balance being inevitable impurities, and T.I. A recycled slag characterized by FeO / Fe ₂ O ₃ ≧ 1.25 in Fe content.

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