JPH11302716A - Production of molten iron dephosphorization slag suitable for recycling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing molten iron dephosphorization slag which forms the molten iron dephosphorization slag to material utilizable as bottoming and civil engineering materials by preventing the powdering of the slag on the premise that the amt. of the fluorite to be used is limited as far as possible. SOLUTION: At the time of executing the dephosphorization treatment of molten iron, converter slag is used as the whole or part of the CaO component in a dephosphorization flux, by which the powdering of the cooling process of the slag formed in the molten iron dephosphorization treatment is suppressed. The CaO component rate of the converter slag in the CaO component in the dephosphorization flux is recommended to be >=20 mass %.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for converting dephosphorized slag generated in hot metal dephosphorization treatment, which is pretreatment of hot metal, which is performed prior to refining in a converter, with materials usable as roadbed materials, civil engineering materials and the like. The present invention relates to a method for producing hot metal dephosphorization slag.

[0002]

2. Description of the Related Art In a converter, decarburization is generally carried out by oxygen blowing, while phosphorus in slag is captured to remove phosphorus. Instead of phosphorus, hot metal dephosphorization is performed, in which hot metal is dephosphorized at a low temperature that is advantageous for the dephosphorization reaction. The dephosphorization flux used for hot metal dephosphorization is mainly composed of iron oxide such as iron ore and scale and quicklime, and the above dephosphorization flux of powder is passed through a lance made of refractory immersed in hot metal. A method of blowing or a method of adding the massive dephosphorizing flux from above the hot metal is adopted.

[0003] The hot metal that has been subjected to the hot metal dephosphorization treatment is subjected to refining mainly for decarburization in the converter in the next process, so that slag conventionally required for dephosphorization can be greatly reduced, and hot metal dephosphorization can be performed. This method can reduce the total flux in the phosphorus process and the converter process.

In order to improve the reaction efficiency of the dephosphorization flux at the time of the dephosphorization, a desiliconization treatment for removing silicon in hot metal is generally performed as a pretreatment for dephosphorization. By the desiliconization treatment, the amount of SiO ₂ generated during the dephosphorization is reduced, the basicity (CaO / SiO ₂ ) of the dephosphorized slag can be increased, and the phosphorus in the hot metal can be reduced to a predetermined phosphorus concentration with a small dephosphorizing flux.

[0005] However, in the slag generated by the hot metal dephosphorization treatment, quicklime added as a dephosphorizing flux does not completely dissolve in the hot metal, and remains in the slag as solid quicklime. The quicklime remaining in the hot metal dephosphorized slag changes into slaked lime when cooled, and at this time the slag is powdered. The powdered slag cannot be used for roadbed materials, civil engineering materials, etc., and is discarded except for being partially used as a cement raw material. In recent years, industrial waste has been taken up as an environmental problem, and it is desired that industrial waste is not generated as much as possible. In particular, recently, environmental measures when treating industrial waste, such as measures to prevent pollution by leachate from industrial waste and measures to prevent scattering of dust, are strictly required, and construction of a new disposal site is extremely difficult. Situation. Therefore,
Recycling of industrial waste is an important issue not only in terms of disposal costs but also in terms of corporate social responsibility.

[0006] The converter slag is used as a roadbed material and a civil engineering material because it has a small amount of undissolved quick lime and does not become powdered even after cooling by a stabilization treatment by steam aging. Therefore, by performing dephosphorization by hot metal pretreatment instead of dephosphorization in the converter, the flux amount and slag amount in the entire treatment process can be reduced as compared with the case of the converter process alone, but the hot metal dephosphorization Since most of the slag had to be discarded, the amount of industrial waste increased, creating a new problem.

In order to improve the reactivity of quicklime in hot metal dephosphorization, fluorite is added to the dephosphorization flux from the viewpoint of improving the solubility of quicklime. However, the fluorite (CaF ₂ ) is desirably as small as possible because it increases the erosion of refractory in a dephosphorization treatment vessel such as a mixed iron wheel, a ladle, a converter, and increases the dephosphorization treatment cost. Component. Furthermore, although there is no regulation in Japan yet, the outflow of fluorine into the soil is subject to environmental regulations in Western European countries, and the increased amount of fluorite in the dephosphorizing flux increases the amount of C in the dephosphorized slag produced.
From the viewpoint of preventing the elution of fluorine in the discarded slag because the aF ₂ content increases, it is desired to reduce the amount of fluorite used in the dephosphorization treatment as much as possible.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended to prevent powdering of hot metal dephosphorization slag on the premise of limiting the amount of fluorite used as much as possible.
An object of the present invention is to provide a method for producing hot metal dephosphorization slag that can be used as a roadbed material or a civil engineering material.

[0009]

Means for Solving the Problems The present invention, which has solved the above-mentioned problems, means that in performing dephosphorization of hot metal, converter slag is used as all or a part of CaO component in the dephosphorization flux to remove hot metal. The purpose of the present invention is to suppress powdering of the slag generated in the phosphorus treatment in the cooling process, and the ratio of the CaO component of the converter slag to the CaO component in the dephosphorization flux is set to 20% by mass or more. Recommended.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Slag produced by hot metal dephosphorization has a high basicity (CaO / SiO ₂ ).
Quick lime added as a dephosphorizing flux is added to hot metal due to the fact that it is treated at a low temperature of about 1300 ° C. compared to a converter exceeding 00 ° C., and that (FeO) in slag is less than that of a converter. It is not completely dissolved and remains in the slag as solid quicklime.

[0011] The present inventors have studied at high temperature and FeO or SiO _2.
The converter slag containing a large amount of components having a high ability to dissolve quicklime, for example, not only has little undissolved quicklime itself, but also has a high ability to dissolve other quicklime. Therefore, by replacing part or all of the quicklime added as dephosphorizing flux in the hot metal dephosphorization treatment with converter slag, the undissolved quicklime content in the dephosphorized slag generated can be significantly reduced. As a result, the present inventors have found that the dephosphorization slag can be suppressed from being powdered and can be sufficiently used for roadbed materials, civil engineering materials, and the like, and the present invention has been completed.

FIG. 1 shows the ratio of the CaO component of converter slag in the CaO component in the dephosphorizing flux (replacement ratio of quicklime in the dephosphorizing flux by converter slag), the concentration of undissolved quicklime in the dephosphorized slag, and Shows the relationship. When a normal dephosphorizing flux to which no converter slag is added is used, about 20% of undissolved quicklime in the slag is present, which is a cause of powdering of the dephosphorized slag. . On the other hand, by replacing about 20% of the lime in the dephosphorized flux with the CaO component of the converter slag, undissolved lime in the slag can be reduced to about 10%, and 50% of the lime in the dephosphorized flux is further reduced. If% is replaced by the CaO component of the converter slag, undissolved quicklime in the dephosphorized slag can be reduced to about 1%.

FIG. 2 shows the concentration of undissolved lime in the dephosphorized slag and the powdered rate of the slag after the dephosphorized slag (5 to 25 mm) has been stabilized by steam aging for 24 hours. Here, the powdering ratio is a weight ratio of a powder component of 74 μm or less. For example, in order to use slag as a roadbed material, it is required that the powdered rate of the slag be about 10% or less in order to obtain an appropriate particle size distribution as the roadbed material.
According to FIG. 2, the concentration of undissolved lime in the slag must be about 15% or less in order to reduce the powdering rate to 10% or less. Furthermore, as shown in FIG. 1, the concentration of undissolved lime in the slag was 15%
It can be seen that the rate of replacement of the quicklime in the dephosphorized flux by converter slag should be at least 20% in order to make the following.
Therefore, in order to make the dephosphorized slag usable as a roadbed material or a civil engineering material, it is desirable that the replacement ratio of the dephosphorized flux medium lime by the converter slag be 20% or more, and more preferably 40% or more. .

[0014] It is disclosed in Japanese Patent Application Laid-Open No. 54-33816, for example, that when converter slag generated during high-temperature converter blowing is used for low-temperature hot metal dephosphorization, it exhibits the dephosphorizing ability again. The technique disclosed in the above publication is intended to reduce the amount of relatively expensive quicklime by replacing quicklime in the dephosphorization flux with converter slag. However, using converter slag for hot metal dephosphorization requires crushing equipment for crushing the solidified converter slag, so using the converter slag also requires new processing costs. Converter slag has not been actively used as a dephosphorization flux.
On the other hand, the present inventors have replaced converter slag with part or all of quick lime added as a dephosphorizing flux to convert dephosphorized slag, which may become a further problem as industrial waste, into civil engineering materials. It has been found that the material can be used as a material, and the present invention has been conceived. Furthermore, due to the excellent quicklime dissolving ability of the converter slag, when converter slag is added to the dephosphorization flux, the amount of fluorite added for the purpose of accelerating the dissolution of quicklime can be reduced, and This method is also preferable from the viewpoint of reducing the amount of fluorine eluted from the slag.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention, and any design change based on the above and following gist will be described. Are included within the technical scope of

[0016]

Example 1 Using the dephosphorizing flux of the conventional example shown in Table 1 and the dephosphorizing flux of Example 1 according to the present invention, the powder of each dephosphorizing flux was mixed with a molten iron through a lance made of refractory. Dephosphorization treatment was performed by blowing into the hot metal in the car together with N ₂ gas at a blowing speed of 500 kg / min for 30 minutes.
The composition of the converter slag used in this example is as shown in Table 2. Therefore, the replacement ratio of quicklime with the converter slag is about 49% as calculated by the following equation.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

(Equation 1)

Table 3 shows the hot metal components before and after the dephosphorization treatment according to the conventional example and the present invention, and Table 4 shows the slag components after the dephosphorization treatment.

[0021]

[Table 3]

[0022]

[Table 4]

The amount of undissolved lime in slag using the conventional dephosphorizing flux is 23.1%, while the amount of undissolved lime in slag dephosphorized by the method according to the present invention is 0.9%, which indicates that the amount of undissolved quicklime can be drastically reduced.

[0024] The powder dephosphorization flux according to the second embodiment of the present invention shown in Example 2 in Table 5, through refractory steel lance torpedo car into the molten iron together with a N ₂ gas, at a blowing rate of 480 kg / min Dephosphorization treatment was performed by blowing for 32 minutes. The composition of the converter slag used in this example is as shown in Table 6, and therefore, the replacement ratio of quicklime with the converter slag is about 42% as calculated by the following equation.

[0025]

[Table 5]

[0026]

[Table 6]

[0027]

(Equation 2)

Table 7 shows the hot metal components before and after the dephosphorization treatment according to the conventional example and the present invention, and Table 8 shows the slag components after the dephosphorization treatment.

[0029]

[Table 7]

[0030]

[Table 8]

As described above, the undissolved lime of the slag using the conventional dephosphorizing flux is 23.1%, whereas the dephosphorizing treatment is performed by the method of the second embodiment according to the present invention. The undissolved lime content in the slag is 1.3%, which indicates that the amount of undissolved lime can be drastically reduced.

For use as a roadbed material or a civil engineering material, it is required that the undissolved lime of the slag be 10% or less, and 3% or less is preferable. The slag subjected to the dephosphorization treatment by the method according to the present invention is a slag that can be sufficiently used as a roadbed material, a civil engineering material, and the like.

[0033]

Since the present invention is constructed as described above, it is possible to prevent powdering of hot metal dephosphorization slag on the premise of limiting the amount of fluorite used as much as possible, and to use it as a roadbed material or a civil engineering material. And a method for producing hot metal dephosphorization slag.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the replacement ratio of quicklime in a flux by converter slag and the concentration of undissolved quicklime.

FIG. 2 is a graph showing the relationship between the concentration of undissolved quicklime in dephosphorized slag and the powdered rate of dephosphorized slag.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kotobuki Yamana 1st Kanazawacho, Kakogawa City, Hyogo Prefecture Inside Kobe Steel Works Kakogawa Works (72) Inventor Reiji Ono 1st Kanazawacho, Kakogawa City, Hyogo Prefecture God Co., Ltd. (72) Inventor Shunichi Toyama 1-3-18 Wakihamacho, Chuo-ku, Kobe Kobe Steel, Kobe Head Office

Claims (2)

[Claims] In the dephosphorization of hot metal, converter slag is used as all or a part of the CaO component in the dephosphorization flux, so that powdering in the cooling process of slag generated in hot metal dephosphorization is performed. A method for producing hot metal dephosphorization slag suitable for use as a material, characterized in that it is suppressed. 2. The method for producing hot metal dephosphorization slag according to claim 1, wherein the CaO component ratio of the converter slag in the CaO component in the dephosphorization flux is 20% by mass or more.