JPH06100919A - Treatment of dephosphorized slag in molten iron - Google Patents

Abstract

PURPOSE:To provide a treating method of slag after executing dephosphorizing treatment in molten iron. CONSTITUTION:The dephosphorizing treatment is executed to molten iron and one or more kinds of metallic Al and metallic Si and material containing them or an alloy containing them are added to the molten slag after separating from the molten iron. By this method, i.e., by using metal reducing agent and simple reducing method, the slag which can effectively be used as roadbed material, etc., has the same strength as natural stone and is low in free CaO, can be obtd. Further, at the same time, a useful iron alloy having high Mn and P contents can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to modifying hot metal dephosphorization slag so that it can be effectively used as a roadbed material, or at the same time as this modification, an iron alloy having a high Mn and phosphorus (P) content is added. The present invention relates to a method for treating dephosphorized slag intended for production.

[0002]

2. Description of the Related Art Conventionally, as a hot metal dephosphorization method, hot metal in a container such as a torpedo car, a ladle, a converter is targeted.
There is a method of injecting a small amount of oxygen (usually about 10 Nm ³ / t) into the hot metal or a method of spraying it onto the hot metal surface together with the dephosphorizing powder of the quicklime-iron oxide-fluorite type.
In addition, as shown in Japanese Examined Patent Publication No. 2-14404, a method of using a vertical blowing converter to top-blend oxygen with a converter slag-based dephosphorizing agent or a quicklime-based dephosphorizing agent is top-added. Has also been put to practical use.

In these methods, the slag after the hot metal dephosphorization treatment is an oxidizing slag containing (FeO), and
Since it contains a very small amount of carbon ([C])-containing granular iron (pig iron), CO gas is generated by the reaction of the following formula (1),
Slag solidifies in the forming state or in the state containing CO bubbles. Therefore, as it is, the strength is weak and it is difficult to effectively use it for roadbed materials.

(FeO) + [C] → CO + Fe (1) Further, such a slag after the hot metal dephosphorization treatment usually has a basicity (hereinafter referred to as CaO / SiO ₂ ) of 2 ~ 3 and lower than that of converter slag (3-5), but still free lime (hereinafter,
It contains about 1 to 5% of free CaO), and if this is used as the roadbed material as it is, there is a problem that this free CaO hydrates and expands due to the reaction of the following equation (2) and cracks occur on the road. It was

CaO + H ₂ O → Ca (OH) ₂ ………………… (2)

[0006]

For the above reasons, the slag after the hot metal dephosphorization treatment cannot be used effectively at all. Therefore, there is a problem that there is no choice but to reclaim the land inside the steelworks and it has become difficult to secure this landfill in recent years.

The present invention reduces free CaO in the slag solidified after the hot metal dephosphorization treatment and imparts strength suitable for roadbed materials, etc. so that it can be effectively used as a construction material for roads and the like. And at the same time with this reform
It was made for the purpose of producing an iron alloy having a high Mn and P content.

[0008]

The gist of the present invention lies in the following method.

[0009] One or more of metal Al, metal Si, a substance containing these or an alloy containing them is added to the molten slag after dephosphorizing the hot metal and separating it from the hot metal. Method for treating hot metal dephosphorization slag.

According to the method of the present invention, after the hot metal dephosphorization treatment, (FeO) in the molten slag separated from the hot metal is "reduced" by a substance containing Al or Si to be modified.
Furthermore, at the same time with this reforming, (MnO), (P ₂ O
₅ ) is “reduced” to produce a useful iron alloy having a high Mn and P content.

Next, the technical idea on which the present invention is based will be described.

As a method for reforming steelmaking slag, research has been conducted on a method of reducing converter slag with carbon and dephosphorizing it. This is intended to solve the problem of converter slag treatment, which had to be landfilled by dephosphorizing the converter slag, recycling it to the blast furnace, and effectively utilizing it as a CaO source.

However, in the case of this method, the converter slag has a high basicity (CaO / SiO ₂ : 3 to 5), and when the (FeO) in this slag is to be reduced with carbon, the reduction reaction proceeds. As (FeO) in the slag decreases, the melting point of the slag rises and the slag solidifies, and the reaction does not proceed on the way. In the converter, high Ca is used for dephosphorization and desulfurization in the furnace.
For O / SiO ₂ operation, CaO slag formation to obtain such high CaO / SiO ₂ forms calcium ferrite with a low melting point (MP about 1200 ° C) with the help of (FeO) formed. It is something that progresses. Therefore, when (FeO) in the slag is reduced by carbon and (FeO) decreases, the melting point of the slag rises and the solidification of the slag occurs, which is unavoidable.

Therefore, in the past, when the converter slag was reduced with carbon, a SiO ₂ source such as silica sand was added to lower CaO / SiO ₂ and the melting point of the slag increased even if the reduction reaction with carbon proceeded. A way to avoid it was considered. However,
This method was possible in the laboratory, but the converter slag contains a large amount of (FeO) at 15 to 25%, and the reaction of reducing this (FeO) with carbon is endothermic. Be a reaction,
In addition to the addition of silica sand and the like, there was a problem that the slag temperature was lowered and the reaction still did not proceed. Therefore, secondary heating was required for heat compensation, but the thermal conductivity of the slag itself was poor,
This heating was not so easy and was not successful as a practical process.

Compared with this converter slag, the hot metal dephosphorization slag has a low CaO / SiO ₂ ratio of 1.5 to 3.0 and a T.Fe content of 3 to 10
%, It is possible to maintain the molten state of the slag with a low melting point (MP <1300 ° C.) even if (FeO) decreases when reducing the slag. Therefore, the reduction is easy and the amount of the reducing agent used is small. In this way, in terms of reducing and reforming slag,
Originally, hot metal dephosphorization slag is easier than converter slag.

The reducing agent may basically be carbon, but it is necessary to compensate the endothermic reaction in this case.
Therefore, there is a method of further blowing carbon and oxygen as a heat source, but it takes a long processing time and causes a problem of forming slag by CO gas at the time of processing. Therefore, it is desirable to use a metal reducing agent that does not generate gas.

[0017]

[Function] As a reducing agent used for slag reforming, metallic Al,
Not only the metal reducing agent such as metal Si itself, but also any substance containing them (of course, Al can as waste may be used). Considering cost especially, aluminum ash generated during smelting of aluminum (Al ₂
O ₃₎ or ferrosilicon (Fe-75% Si) are preferred. In particular, in the case of ferrosilicon, in order to increase the reaction rate, it is preferable to use crushed particles having a particle size of 10 mm or less.

Since these have a higher reducing ability than [C] in granular iron, the reaction of the following equations (3) and (4) causes
Although (FeO) is reduced, all the reactions are exothermic reactions, so that not only can the temperature drop during the treatment be compensated, but the slag temperature can be increased. Furthermore, since no CO gas is generated, the slag does not solidify in the forming state or in the state containing gas bubbles. Therefore, a solidified slag with high strength and high density that can be effectively used as a roadbed material or the like can be obtained.

3 (FeO) + 2Al → Al ₂ O ₃ + 3Fe (3) 2 (FeO) + Si → SiO ₂ + 2Fe (4) That is, when a reducing agent is added, first, (3), (FeO) is reduced by the reaction of the formula (4) (Thermit reaction), and the temperature of the slag rises due to the exothermic reaction. For example, Al ash (4
10% per ton of dephosphorized slag when 0% Al) is used
It increases by about 20 ° C with the addition amount of. No heating is required to compensate for the temperature drop during processing due to this heat.

In the case of the equation (3), this heat generation and the generated Al
₂ O ₃ and Al ₂ O ₃ in the added aluminum ash reduce free CaO in the dephosphorization slag. This means that Al ₂ O ₃ is CaO
Reacts with, and produce a CaO-Al ₂ O _3, in order to fix the CaO. The free CaO after this reduction reforming treatment varies depending on the amount of reducing agent added, but the fr
When ee CaO is 1 to 5%, it decreases to 1 to 2% or less.
Therefore, the obtained solidified slag has a low free CaO content to such an extent that the hydration expansion reaction of the formula (2) hardly progresses even when used as a roadbed material.

When ferrosilicon, for example, is used as the reducing agent, it is an exothermic reaction as in the case of using the above-mentioned Al ash, and since SiO ₂ is produced by the formula (4), the slag basicity after the treatment is lowered, The melting point also decreases. As a result, free CaO dissolves in this slag, and free CaO is similarly reduced.

The amount of the reducing agent to be added is tentatively determined so that the forming of the slag can be calmed down after the dephosphorization treatment and the solidified slag has a strength that can be used for the roadbed material. For example, if (FeO) in the slag before treatment is 3%, the minimum required amount per ton of dephosphorized slag is 5 kg (50
% Al ash is 10 kg), and the pure Si content is 4 kg (Fe-75% Si, 5.3 kg). Needless to say, the required addition amount depends on the content of (FeO) in the dephosphorization slag before treatment.

The upper limit of the amount of reducing agent added is not particularly limited. If the amount of reducing agent added exceeds the amount sufficient to reduce (FeO), (P ₂ O ₅ ) and (MnO) in the dephosphorized slag are also reduced, resulting in the formation of Fe-Mn-P alloy. To do. This alloy is effective as ferroalloy like ferroline (Fe-P). Therefore, it is also possible to add a large amount of reducing agent to positively generate this alloy, and to separate and recover this alloy from the reformed slag for use.

The addition method of the reducing agent may be a simple placing method, but from the viewpoint of preventing the scattering loss of the reducing agent at the time of feeding and ensuring the uniformity of the obtained slag, a powdery or granular material is used. A method of injecting the molten slag into the molten slag using N, N ₂ or Ar is also effective.

In the case of this method, a reducing agent which is more expensive than carbon such as Al and Si is used, but T.Fe is used in the hot metal dephosphorization slag.
Since its average value is as low as about 4%, the amount of the reducing agent used does not become so large as to increase the treatment cost when it is intended only for the slag reforming treatment, and it is not a critical problem.

As a method for reducing the dephosphorized slag, any method may be used as long as it is a method of adding a reducing agent to the molten slag and stirring them. For example, the following method can be considered.

(1) A method of reducing in a slag jar (or similar container).

After the hot metal dephosphorization treatment, the slag is transferred to a slag jar, a reducing agent is added to the slag, and N ₂ and Ar gas are blown into the slag and the mixture is stirred. In particular, when the dephosphorization treatment is carried out in a converter type furnace, if a reducing agent is added to the falling stream flowing out to the slag jar, the reduction reforming can be performed only by the stirring force at this time. of course,
Further, in order to ensure the uniformity of the slag, N ₂ or Ar gas may be blown into the slag in the slag jar for gas bubbling. The slag jar may be made of cast iron, but it is easier to prevent the temperature from dropping if the refractory is lined.

(2) Method of reduction in hot metal dephosphorization treatment vessel When hot metal dephosphorization is performed in a converter type furnace or torpedo car, after dephosphorized hot metal is tapped, dephosphorization left in the converter or torpedo car Add a reducing agent to the slag,
A method of bubbling stirring by blowing gas such as N ₂ or Ar. The bottom gas bubbling method is used in the case of a converter, and the gas injection method using an injection pipe is used in the case of a torpedo car.

[0030]

【Example】

(Example 1) A 250t converter having both upper and lower blowing functions was used as a dephosphorization furnace, and hot metal (C: 4.5%, Si: 0.15%, Mn: 0.
33%, P: 0.110%, S: 0.025%, temperature 1330 ℃) with a dephosphorizing agent (converter slag 25 kg / t, pig iron ore 10 kg / t and fluorspar 5 kg / t generated during de-P hot metal blowing) After the addition, oxygen of 7 Nm ³ / t was top-blown from the top-blown lance, and dephosphorization treatment was carried out for about 10 minutes. The amount of slag produced at this time was 40 kg per ton of hot metal.

The obtained hot metal (C: 4.0%, Si: trace, Mn: 0.20%, P: 0.020%, S: 0.015%, temperature 13
(50 ℃) After tapping the hot water into the ladle, when tapping the dephosphorized slag into the slag jar, 30 kg of aluminum ash (50% Al-Al ₂ O ₃ ) per ton of slag is discharged as a reducing agent. It was added so as to be caught in the flow. After the dephosphorized slag was discharged to the slag jar, using an iron pipe coated with alumina, N ₂ 25Nm ³ / mi
N was bubbled in and stirred for 3 minutes. Table 1 shows the slag components and temperatures before and after the modification treatment.

As shown in Table 1, the free CaO of the slag obtained after solidification decreased from 4.1% to 0.2%. In the cutting investigation after crushing, no forming state (air bubbles) was observed at all, and it was as dense as natural stone. The crushed massive slag was used as a roadbed material in a steel mill, and as a result, no cracks were found on the road even after 4 years.

[0033]

[Table 1]

(Example 2) As in Example 1, a 250t converter having both upper and lower blowing functions was used as a dephosphorization furnace, and hot metal was used.
(C: 4.6%, Si: 0.16%, Mn: 0.32%, P: 0.112
%, S: 0.027%, temperature 1340 ° C), after adding a dephosphorizing agent (converter slag 25 kg / t, iron ore 15 kg / t and fluorspar 4 kg / t), oxygen 6 Nm ³ / t was supplied from the top blowing lance. Top spraying and dephosphorization treatment were carried out for 11 minutes. The amount of slag produced at this time was 40 kg per ton of hot metal.

The obtained hot metal (C: 4.1%, Si: trace, Mn: 0.19%, P: 0.023%, S: 0.020%, temperature 13
(40 ° C) After tapping the hot water in the ladle, Fe-Si (75% Si) is put in the furnace.
20 kg per ton of slag, 50 Nm ³ / min from the bottom of the furnace
N ₂ gas was blown in and the mixture was stirred for 5 minutes. The obtained slag was poured into a slag jar and then solidified as it was. Table 2 shows the slag components and temperatures before and after the modification treatment.

The state of free CaO and bubbles in the slag after solidification,
And, the results of the trial use of the crushed massive slag as a roadbed material in the steel mill were exactly the same as in Example 1.

[0037]

[Table 2]

(Example 3) 160 tons of hot metal charged in a hot metal ladle
(C: 4.7%, Si: 0.16%, Mn: 0.26%, P: 0.105
%, S: 0.025%, temperature 1390 ℃, dephosphorizing powder (quick lime)
(17 kg / t, iron ore 20 kg / t, fluorspar 5 kg / t) is injected into the hot metal with N ₂ gas carrier using an alumina coating pipe, and 6 Nm ³ / t of oxygen is top-blown using a top blowing lance. Then, dephosphorization treatment was carried out for 18 minutes.

After the treatment, when the dephosphorized slag was discharged into a slag jar with a slag dragger, shot aluminum having a particle size of about 10 mmφ was added in an amount of 50 kg per ton of slag. The amount of slag produced at this time was about 35 kg per ton of hot metal.

After completely discharging the dephosphorized slag into the slag jar,
Using an alumina-coated iron pipe, N ₂ gas of 10 Nm ³ / min was blown into the slag, and the mixture was stirred for 5 minutes and solidified as it was. Table 3 shows the hot metal components and temperatures after the treatment.
The slag component and the temperature before and after the reforming treatment are shown in each.

The obtained slag has no forming even in a molten state, and the solidified slag is dense and free C like natural stone.
A low aO was obtained. As a result of using the crushed slag as a roadbed material in the steel plant, no cracks were found on the road even after 3 years.

When the solidified slag was crushed to form a roadbed material, about 40 kg of lumps could be separated per ton of slag.
As a result of analyzing this lump, it was an Fe-Mn-P alloy having the chemical composition shown in Table 5. It is considered that this alloy also contains granular iron in the slag.

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

[Table 5]

[0046]

According to the method of the present invention, the hot metal dephosphorization slag, which had hitherto been used only for landfill without any effective utilization method, can be treated with a metal reducing agent and a simple reducing method in the same manner as natural stone without slag foaming. It is possible to modify slag with low strength and low free CaO so that it can be effectively used as a roadbed material. Furthermore, it is possible to simultaneously produce a useful iron alloy having a high Mn and P content.

Claims (1)

[Claims] 1. The molten slag after dephosphorizing the hot metal and separating it from the hot metal is added with one or more of metal Al, metal Si, a substance containing them, or an alloy containing them. A characteristic method for treating hot metal dephosphorization slag.