JPS642650B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a regeneration method for reusing slag after dephosphorization treatment. Conventionally, various attempts have been made to regenerate a dephosphorizing agent from slag after dephosphorizing molten iron. For example, as a method to regenerate soda ash from soda slag obtained by dephosphorizing molten iron using soda ash (Na ₂ Co ₃ ), a wet recovery method has been partially implemented in which soda ash is recovered by dissolving soda slag in water. . However, wet recovery methods require special equipment and are not efficient. Efforts have also already been made to dephosphorize converter slag by carbon reduction at high temperatures and reuse it as a converter slag forming agent or blast furnace raw material (mainly sintering raw material). 1600
In the case of carbon reduction at a temperature (℃), P ₂ O ₅ is reduced after the iron oxide (FeO) in the slag is reduced and reduced. However, in the case of slag such as converter slag, which contains few solvents such as CaF ₂ and has a basicity (CaO/SiO ₂ ) of 3 or more, the melting point of the slag increases as the iron oxide decreases, causing the slag to harden. There is a problem in that the reduction reaction does not substantially proceed because the molten state cannot be maintained. Furthermore, in order to prevent such an increase in the melting point, a method of adding a SiO ₂ source such as silica stone is also being considered. However, in this case, although dephosphorization is easy, there is a problem that the recycled slag has a low basicity and has little utility value. On the other hand, as a dephosphorization method for molten iron, especially molten iron containing Cr, the normal oxidative dephosphorization method
is preferentially oxidized, the melting point of the slag increases and dephosphorization hardly progresses. The inventors are Cr
As a method for dephosphorizing molten iron containing molten iron, a flux consisting of one or more alkaline earth metal oxides and one or more alkaline earth metal halides is added, and an amount of flux that does not harden the slag produced is added. proposed a dephosphorization method by adding an oxidizing agent (Patent Application Reference 57-
33549). This dephosphorization method removes alkaline earth metal oxides.
A method of dephosphorizing by blending 30 to 60% and 40 to 70% of halides to make the melting point below the dephosphorization treatment temperature (approximately 1450 ° C.), and adding an appropriate amount of oxidizing agent,
This is an effective method for dephosphorizing molten iron containing Cr, such as stainless steel. However, when BaO is used as an oxide of an alkaline earth metal, or when BaCl ₂ is used as a halide of an alkaline earth metal, they are expensive and have the disadvantage of high flux costs. Moreover, since BaO is not commercially available other than pharmaceutical grade, it is common to use BaCO ₃ or Ba(OH) ₂ . In these cases, if added to molten iron alloy or molten Ni-based alloy, it will thermally decompose.
BaO is formed, but it also has the drawbacks of lowering the temperature of the molten metal due to the endothermic reaction caused by decomposition, and the flame is large. This invention eliminates these drawbacks and provides a regeneration method that removes phosphorus from slag after dephosphorization treatment and regenerates it into dephosphorization flux. Carbonaceous material or carbon is added to the slag obtained by dephosphorizing molten iron alloy or molten Ni alloy using a flux consisting of a substance, an alkaline earth metal halide, and an oxidizing agent, the melting point of which is below the dephosphorization treatment temperature. Add molten iron containing
It is characterized in that the treatment is carried out at a temperature equal to or higher than the dephosphorization treatment temperature. That is, this invention uses the dephosphorization method proposed earlier and a similar flux to reduce and remove phosphorus from the slag generated by dephosphorizing molten iron that does not contain Cr, and regenerate it as a flux for dephosphorization. be. Therefore, it also includes cases where alkaline earth metal carbonates or hydroxides are used instead of alkaline earth metal oxides, and the oxidizing power of the alkaline earth metal carbonates is used as an oxidizing agent. This also includes cases where In addition, the molten metal targeted for dephosphorization is a molten iron-based alloy or a molten Ni-based alloy, such as Cr, Ni,
The present invention also applies to slag obtained by dephosphorizing molten metal containing 30% or less of Mn. The slag after these dephosphorization treatments generally contains one or more alkaline earth metal oxides, one or more alkaline earth metal halides, oxidizing oxides, P ₂ O ₅ and , and others are included. Oxidants with oxidizing power include Cr oxide, MnO,
FeO, etc., and is determined by the oxidizing agent used, the molten metal to be dephosphorized, and the alloy components contained therein. For example, oxides used as oxidizers may remain in the slag,
If O ₂ gas or CO ₂ generated by thermal decomposition of carbonate is used as the oxidizing agent, or if iron oxide is used, and the molten metal contains a large amount of Cr or Mn, the following reaction will take place: _{Cr2O3 or} MnO
may be included in the slag after this dephosphorization treatment. 3FeO＋2Cr→Cr ₂ O ₃ +3Fe ……(1) O ₂ ＋2Mn→2MnO ……(2) In addition, the others in the above slag components include Si in the molten metal that is oxidized to become SiO ₂ , and desulfurization. This includes S that has entered the slag due to the reaction, and MgO that has entered the slag due to melting of the furnace body. In the case of the above-mentioned dephosphorization method, the oxidizing power of the slag is
higher than that corresponding to the carbon content of the molten metal,
In other words, this dephosphorization method takes advantage of the delay in decarburization and artificially increases the oxidizing power of slag to effectively dephosphorize it. The present inventors focused on this, and conversely, if the slag after dephosphorization treatment is heated to a temperature higher than the dephosphorization treatment temperature together with carbonaceous substances, oxidizing oxides (FeO, MnO, Cr ₂ We found that carbonaceous substances (O ₃ , etc.) were easily reduced by carbonaceous substances. As a result, P ₂ O ₅ in the slag is also reduced to P, which is mainly absorbed by metals such as Fe, Mn, and Cr produced by the reduction, and the slag with low phosphorus content is regenerated. In addition, even if molten iron containing carbon that is higher than the carbon content of the molten metal to be dephosphorized, such as hot metal that has been desiliconized in advance, is added instead of the above carbonaceous material, the oxidizing power will be the same as when carbonaceous material is used. oxide (FeO,
MnO, Cr ₂ O _3, etc.) are ring-formed by C in the molten iron and absorbed into the molten iron. P ₂ O ₅ in the slag is also reduced to P and enters the molten iron. The reaction is according to the following formula. C+FeO→CO+Fe......(3) C+MnO→CO+Mn...(4) 3C+Cr ₂ O ₃ →3CO+2Cr...(5) 5C+P ₂ O ₅ →5CO+2P...(6) In this case, the molten iron does not contain much Si. It is better if it is not. This is because, in the case of molten iron containing Si, the dephosphorization slag can be reduced, but mainly Si acts to become SiO ₂ and enter the slag, reducing its basicity. Such a reaction will occur if the treatment temperature is higher than the dephosphorization treatment temperature, but the higher the temperature, the easier it will be. Further, the higher the carbon mass and the carbon content of the molten iron, the better the results. Further, in order to speed up the reduction reaction, it is necessary to perform stirring. Any method may be used for stirring, such as gas bubbling using Ar or N ₂ gas, or mechanical stirring using an impeller. The obtained recycled slag is mainly composed of alkaline earth metal oxides and alkaline earth metal halides, and is recycled as a dephosphorization flux with extremely low oxidizing oxides and P ₂ O ₅ . It is something that The regenerated slag is used again for dephosphorizing molten metal with the addition of new oxidizing agent. By the method of the present invention, even expensive fluxes can be used repeatedly, making it possible to perform low-cost dephosphorization treatment. Examples and comparative examples will be explained. Example 1 2 kg of molten iron containing chromium was produced using a Tammann furnace.
After dissolving in the atmosphere in a MgO crucible and maintaining the temperature at 1450°C, 200g of flux consisting of 40% BaO and 60% BaCl ₂ was added, and 10g of Cr ₂ O ₃ was dispensed as an oxidizing agent while stirring with a magnesia impeller. death,
Treated for 15 minutes. Table 1 shows the molten iron components before and after treatment.

[Table] The treated slag was charged into an MgO crucible together with 10 g of carbon, and stirred for 30 minutes by Ar bubbling while maintaining the temperature at 1600°C in a Tamman furnace.
Table 2 shows the slag components before and after the reduction treatment.

[Table] As is clear from Table 2, as a result of implementing the present invention, Cr ₂ O ₃ and T.Fe in the slag were reduced and decreased, and P ₂ O ₅ was also reduced and decreased. Molten iron was dephosphorized using the obtained slag. 150g of the obtained slag and 2kg of molten iron containing chromium were mixed with MgO
Charge it into a crucible and melt it using a Tammann furnace.
Table 3 shows the molten iron components before and after the treatment, in which 10 g of Cr ₂ O ₃ was added in portions while stirring with a magnesia impeller and dephosphorized for 15 minutes while maintaining the temperature at 1450°C.

[Table] As is clear from Table 3, when the slag regenerated by the method of this invention was used again as a dephosphorization flux, dephosphorization progressed to the same extent as in Table 1. Example 2 2 kg of a Ni-based alloy containing chromium was melted in the atmosphere in an MgO crucible using a Tammann furnace and maintained at a temperature of 1450°C, after which 22 g of a flux consisting of 46% BaCO ₃ and 54% BaCl ₂ was poured into the melt. Stirred with a magnesia impeller. Table 4 shows the composition of the Ni-based alloy before and after treatment for 15 minutes.

[Table] The treated slag was maintained at a temperature of 1600°C in an MgO crucible using a Tammann furnace, 1 kg of molten iron containing carbon was added, and the mixture was stirred for 30 minutes by Ar bubbling. Table 5 shows the components of the slag before and after treatment.
Table 6 shows the components of the carbon-containing molten iron before and after treatment.

【table】

[Table] As can be seen from Tables 5 and 6, as a result of reducing slag with carbon-containing molten iron after dephosphorization treatment,
Cr ₂ O ₃ and T.Fe in the slag were reduced and entered the molten iron, and P ₂ O ₅ was also reduced and turned into P and entered the molten iron, thus regenerating slag with a low P content. The obtained slag was used to dephosphorize a Ni-based alloy. Melt 2 kg of Ni-based alloy in a magnetic crucible using a Tammann furnace, add 150 g of the obtained slag, and while stirring with a magnesian impeller.
7 g of Cr ₂ O ₃ was dispensed. The processing temperature was 1450℃.15
Processed for minutes. Table 7 shows the composition of the Ni-based alloy before and after treatment.

[Table] As can be seen from Table 7, the slag regenerated by the method of the present invention had a sufficient dephosphorizing effect as a flux for dephosphorizing Ni-based alloys. Example 3 2 kg of hot metal that had been desiliconized in advance was used in a Tammann furnace.
After atmospheric dissolution in a MgO crucible and kept at a temperature of 1300℃, CaO30%, _CaCl2 40%, _CaF2 10%,
200 g of flux containing 20% Fe ₂ O ₃ was added and stirred for 15 minutes using a magnesia impeller to perform dephosphorization treatment. Table 8 shows the hot metal components before and after treatment.

[Table] The treated slag was charged into a graphite crucible, 30 g of carbon was added while maintaining the temperature at 1600°C in a Tammann furnace, and reduction treatment was performed by Ar bubbling for 30 minutes.
Table 9 shows the slag components before and after treatment.

[Table] Hot metal was dephosphorized using the obtained recycled slag. Hot metal that had been desiliconized in advance was melted in an MgO crucible using a Tammann furnace, 130 g of the obtained slag was added, the temperature was maintained at 1300°C, and 25 g of Fe ₂ O ₃ was added while stirring with a magnesia impeller. The mixture was stirred for 20 minutes. Table 10 shows the hot metal components before and after treatment.

[Table] As shown in Table 10, the slag recycled by the method of this invention was reused as a flux for dephosphorizing hot metal, and good results were obtained. Comparative example: 2 kg of molten iron containing chromium was produced using a Tammann furnace.
A flux consisting of 40% BaO and 60% BaCl ₂ dissolved in the atmosphere in a MgO crucible and maintained at a temperature of 1450°C.
Table 11 shows the components of the molten iron before and after the dephosphorization treatment, in which 200 g of the molten iron was added, and 10 g of the oxidizing agent was added in portions for 15 minutes while stirring with a magnesia impeller.

[Table] The treated slag was kept at a temperature of 1450°C in an MgO crucible using a Tammann furnace. Molten iron having approximately the same carbon content as the dephosphorized molten iron was added to this. Table 12 shows the components of the added molten iron.

[Table] Table 13 shows the molten iron components before and after stirring for 1 hour using a magnesia impeller at 100 rpm.

[Table] As is clear from Table 13, when the carbon content of the molten iron containing carbon for slag regeneration is the same as the carbon content of the dephosphorized molten iron, and the regeneration treatment temperature is the same as the dephosphorization treatment temperature. Even after one hour of treatment, there was almost no reduction, and P in the slag was not removed. That is, the carbon content of the carbon-containing hot metal of the present invention needs to be higher than the carbon content of the dephosphorized molten iron or Ni alloy, and the regeneration treatment temperature needs to be performed at a higher temperature than the dephosphorization treatment temperature. As described above, the present invention provides a method for regenerating P by reducing and removing it from slag after dephosphorization treatment, even when the flux uses expensive alkaline earth metal oxides and halides. Since it is also reused, it has a great effect in reducing the cost of dephosphorization.

Claims (1)

[Claims] 1 Slag obtained by dephosphorizing molten iron alloy or molten Ni alloy using dephosphorization flux consisting of alkaline earth metal oxide, alkaline earth metal halide, and oxidizing agent and having a melting point below the dephosphorization treatment temperature. A method for regenerating dephosphorization slag, which comprises adding carbonaceous or carbon-containing molten iron to the slag and treating at a temperature equal to or higher than the dephosphorization temperature.