JPS61213309A - Manufacture of flux for refining using molten pig iron dephosphorization slag as starting material - Google Patents

Abstract

PURPOSE:To manufacture a flux for refining having proper characteristics for each use by adding one or more kinds of modifiers selected among SiO2, Al2O3, CaF2, Al and Al compounds as well as a carbonaceous reducing agent to molten pig iron dephosphorization slag to carry out melt reduction and modification. CONSTITUTION:One ore more kinds of modifiers selected among SiO2, Al2O3, CaF2, Al and Al compounds as well as a carbonaceous reducing agent are added to molten pig iron dephosphorization slag at >=500 deg.C to carry out melt reduction and modification. Since the selected modifiers are added, a flux for refining having a proper composition and proper characteristics for each use is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a refining flux using dephosphorized hot metal slag as a raw material.

(Prior Art) Hot metal dephosphorized slag has a characteristic of having higher P2O than converter slag, but since the P20!1 contained in phosphorus fertilizer is not found in phosphorus fertilizer, it cannot be used as is as phosphorus fertilizer.

In addition, some ordinary converter slag is used for road materials and civil engineering materials, but dephosphorized slag has a high c, o/SiO□ content and is highly collapsible, so it cannot be used for such purposes.

On the other hand, demand for refining flux used in processes such as hot metal pretreatment, converter blowing, secondary refining, and continuous casting is on the rise due to quality needs in steelmaking. Against this background, various attempts have been made to recycle dephosphorized hot metal slag. For example, dephosphorization slag is crushed and separated into parts with high and low concentrations of p and os using the flotation method.
A method of effectively using the high 2O content for phosphorus fertilizer and the low 2O content for blast furnace raw material (Japanese Patent Application Laid-open No. 58-61210), and dephosphorization.
DeP by adding carbonaceous or carbon-containing molten iron to slag
A method has been proposed (Japanese Unexamined Patent Publication No. 59-53637) in which slag is recycled into flux for removing P after performing a reduction treatment at a temperature higher than the treatment temperature and transferring P into the molten iron.

(Problems to be Solved by the Invention) However, the former method is inefficient because it is necessary to crush the slag into small pieces for flotation. In addition, even if the P concentration is low, it is not low enough to be used as a scouring aid, so there is a problem that its use, for example, as a blast furnace raw material, is limited. on the other hand,
The latter is a dephosphorization process using a special low-melting-point deS7 laxative made of alkaline earth metal oxides and halides.
It is intended for slag and cannot be used for CaO-based hot metal dephosphorization slag. Further, although these are methods for dephosphorizing and regenerating slag, they do not attempt to actively control the slag composition and characteristics after dephosphorization.

(Means for Solving Problems) The present invention melts and reduces this hot metal dephosphorization slag to remove P and actively modifies it to produce a refining flux with an appropriate composition and characteristics for each use. Its purpose is as follows.

While adding a carbonaceous reducing agent to hot metal dephosphorization slag at 500°C or higher, on the other hand, 5102, A1. O3, C, F...
1. A method for producing a refining flux, which comprises selectively adding one or more modifiers selected from M and a modifier made of its compound to perform melt reduction treatment and modification treatment.

(effect) The details of the present invention will be explained below.

There are many types of refining fluxes used in the steelmaking process, such as S-free fluxes, S7-free fluxes, and antioxidants, each of which has an appropriate composition and characteristics depending on its use. To give a specific example, the ladle flux and continuous casting powder base material for the purpose of preventing oxidation of the hot water surface, adsorbing inclusions, etc. are non-oxidizing and have a low melting point composition with CaO/5i02 around 1.0. is preferred, and the S removal flux is CaO/Ag2O
3 is around 1.0 or 3.5, and a non-oxidizing, low melting point composition is also desired. In addition, with the development of hot metal pretreatment, the amount of slag in converters is decreasing, and the role of prevention of fume generation and spitting is becoming more important than the conventional purpose of removing P and S, and recycled slag is also suitable for these purposes. something is wanted.

On the other hand, in order to recycle slag, it is first necessary to remove P. Dephosphorization from slag is relatively easy through carbon reduction at high temperatures, but in the past, a large amount of P was transferred to molten iron;
There was a problem in handling high phosphorous molten iron. In this regard, the present inventor separately developed a method for separating and recovering individual P from hot metal dephosphorized slag. This method minimizes the amount of P that transfers to molten iron during slag reduction, and the element P that becomes gaseous.
This system is characterized by increasing the generation ratio of MnO and recovering it, increasing the MnO content of hot metal dephosphorized slag from 5% to 12%.
A method of melting and reducing the P by adding a carbonaceous reducing agent and selectively adding a P separation accelerator consisting of 5i02, Alto, and compounds thereof. The separation accelerator is the same as the modifier for refining flux. Therefore, in addition to recovering P, it is considered to be extremely economical and preferable to reform the dephosphorized hot metal slag into a refining flux.

The present inventor has focused on this, and has carried out numerous dephosphorization processes using modifying materials such as soft silica stone and M fluorite.
We conducted a modification experiment and obtained the following results. That is, an appropriate amount of carbonaceous reducing agent and 5i02 are added to the hot metal dephosphorization slag.
, Al2O3, M-, CaF2, and their compounds. When one or more modifiers are selectively added to the melting reduction treatment and modification treatment, the slag dephosphorization rate is determined by the slag composition after the addition of the modifier. It turned out that it was possible to organize it well.

According to Figure 1, the refining flux, e.g. Cαo/51
Ladle flux and CaO/Al with o2 around 1.0
It is known that a S-removal flux with 2O3 of around 1.0 has an appropriate composition from the viewpoint of slag removal and is extremely convenient. Also, for example, Ca O/Si 02 =3.0
Front and rear sludge accelerators and Ctz O//A1203
” When producing dephosphorized 87 lux of around 3.5, it is possible to improve the dephosphorization rate by adding some AltOsk to the former and some 8102 to the latter.

The present invention is based on this experimental result, and is a method for manufacturing flux for refining by reducing Pf from hot metal dephosphorization slag and reforming the slag by actively adjusting the components. The composition adjustment of the reforming tank can be calculated from the composition of the modifier to which the hot metal dephosphorization slag is added, and similarly, the melting point adjustment can be done using CcO-A1203 series, CaO
-5i02 Practically desired compositions and properties can be added by predicting from a multicomponent system phase diagram such as CaF2 system.

The refining flux obtained in this manner is non-oxidizing due to the reduction treatment, and is molten, so the quality is homogeneous. The implementation and use of the present invention provides the following advantages.

(1) Hot metal arm P slag, which has traditionally been difficult to dispose of, can be used completely effectively.

(2) Refining flux can be supplied within the plant, reducing costs.

(3) The use of ladle flux improves alloy yield, especially M yield.

(4) Converter recycling promotes slag formation at the initial stage of blowing, and thus improves the collapsibility of converter slag.

Next, processing cost becomes a problem because a large amount of energy is required to reduce and reform hot metal arm P slag, but in order to solve this problem, the present invention uses hot metal arm P slag as a raw material. It is characterized in that it is charged into a melting reduction furnace at a temperature of 500°C or higher or in a molten state. When we performed a thermal calculation and looked at the energy distribution, the heating and melting of the raw material slag accounted for approximately 45%.
It was found that the heat rise and melting of the modifier accounted for approximately 23%, and the reduction heat of FelMn, P, etc. accounted for approximately 23%, so we measured the dephosphorization slag temperature with the aim of utilizing the sensible heat of the dephosphorization slag. I did it. When slag 6T is discharged into an iron container, the temperature at the center of the slag is 1100-1200℃ immediately after discharge, 1020-1150℃ after 5 hours, and 1000℃ after 10 hours.
~1100°C, confirming that the temperature drop was small. Even if operational fluctuations such as slag discharge amount and transportation time are taken into account, it is fully possible to charge dephosphorized slag into a smelting reduction furnace at a temperature of 500° C. or higher. On the other hand, when the charging temperature is below 500°C, the sensible heat utilization effect is small. Also, depending on the conditions, the dephosphorized slag may be discharged in a molten state, but it is natural that the sensible heat utilization effect will be greater if it is charged in a molten state. De-P
By charging the slag at 500° C. or higher or in a molten state, the thermal energy required for melting reduction and reforming treatment can be reduced by 15 to 43%, which has a large economic effect.

(Example) Next, examples of the present invention will be described.

Using an electric furnace with a capacity of 500 KVA, hot metal arm P slag having the composition shown in Table 1 was melted and reduced according to the composition shown in Table 2 to remove P and undergo reforming treatment. Table 3 shows the composition, dephosphorization rate, and softening point of the finished slag. Table 2 also shows formulation goals and applications.

By adjusting the blend of raw materials in Table 1, the C, O/
5102 and CaO/Al2O3, and is affected by the softening point, but all of them are largely removed and can be used as a refining flux and its base material, such as as a hot water surface oxidation inhibitor and for removing SNJ. .

(Effects of the Invention) As described in detail above, the present invention provides a practical method for reducing P-removal of hot metal dephosphorization slag and performing reforming treatment to produce refining flux' at low cost. It is something to do. In addition, in the reduction treatment and reformation treatment,
It is effective to use gas stirring together.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the formation of hot metal dephosphorized slag in melting reduction. Roasted Amata Giryo Preparation

Claims (1)

[Claims] A carbonaceous reducing agent is added to hot metal dephosphorization slag at 500°C or higher, while SiO_2, Al_2O_3, CaF
_2. A method for producing a refining flux, characterized in that one or more modifiers selected from among modifiers consisting of Al and its compounds are selectively added to perform melting reduction treatment and modification treatment.