JPH11158526A - Production of high p slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining a high P slag which can be directly used as a fertilizer containing 10-35% P2 O5 by using molten iron having <=0.15% P concn. as the starting raw material. SOLUTION: This method is constituted of a first process for producing high P molten iron 4 containing 0.5-3% P and <=0.1% Si obtd. by reduction- extraction from the slag obtd. by executing the dephosphorization treatment to the molten iron having <=0.5% P concn., and a second process for adding flux 8 into this high P molten iron so that the slag basicity becomes 2-8 and executing oxidation refining till becoming <=1% carbon concn., to obtain the high P slag having 10-30% P2 O5 concn. After executing the first process, Mn and Si in the high P molten iron are lowered and thereafter, the treatment in the second process is executed to obtain the high P slag having 10-35% P concn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
% Or less of low-P hot metal as a starting material and a high concentration of P ₂ O ₅
And a method for producing high-P slag that can be used directly as a fertilizer.

[0002]

_2. Description of the Related Art As a method for obtaining a slag having a high P ₂ O ₅ , the Thomas converter method using hot metal containing P of 1.5 to 2% (hereinafter, all concentrations are shown by weight%) is an old method. Known from.

[0003] However, judging from the current raw material situation, the P concentration in the hot metal is 0.15% or less, and the adoption of the Thomas converter method is not practical. Also, in the case of the Thomas converter method, about 0.5% of Si is contained in the hot metal, and the amount of slag is as large as 200 to 300 kg per ton of molten steel,
The P concentration is high despite of the hot metal, P ₂ O ₅ is 16 to 22
In percent.

Japanese Patent Application Laid-Open No. Hei 7-316621 discloses that
By reducing P ₂ O ₅ contained in the slag several times, P in the hot metal is concentrated to about 1 to 3%, the hot metal is removed again with a small amount of slag, and the slag having a high P ₂ O ₅ is obtained. Have been proposed.

[0005]

However, the above proposal is
It is hard to say that the optimum flux composition and hot metal removal P conditions for obtaining a slag with a high P ₂ O ₅ are clarified.

An object of the present invention is to use a low P molten iron having a P concentration of 0.15% or less as a starting material, wherein P ₂ O ₅ is 1%.
It is an object of the present invention to provide a method for obtaining high P slag which can be directly used as a fertilizer containing 0 to 30%, and in claim 2, 10 to 35%.

[0007]

The present inventor has made various studies to achieve the above object, and as a result, the following (A) to
(D) was obtained.

[0008] (A) Starting from a low P hot metal having a P concentration of 0.15% or less, slag produced by removing P from the hot metal is put into a vessel containing a hot metal bath, and the carbon material and iron oxide When the P-containing slag is melted by supplying oxygen and / or oxygen, hot metal containing 0.5 to 3% of P can be obtained. The Si concentration of this hot metal is 0.1% or less, while containing P equivalent to the hot metal used in the Thomas converter method,
Unlike the Thomas converter method, the Si concentration is low. Therefore, the amount of slag at the time of removing P from the hot metal again (hereinafter referred to as final removal P) can be reduced, and a slag having a high P ₂ O ₅ can be obtained.

(B) If the carbon concentration is reduced to 1.0% or less during the final degassing, the temperature of the molten steel rises due to the heat of combustion reaction of carbon and becomes 1550 ° C. or more. Even without the addition of stone (CaF ₂ ), the slag can be sufficiently dissolved to form a slag having a strong de-P force. (C) The effect of the above (B) can be further enhanced by properly managing the slag basicity at the time of the final de-P.

(D) The hot metal bath contains 0.5 to 3 as described above.
% Of P, but at the same time contain approximately the same concentration of Mn and about 0.1% of Si. At the time of the final removal of P, at the same time as P transfers to slag, Mn and Si also transfer to slag in the form of MnO and SiO ₂ . When slag is used as fertilizer, M
Although nO and SiO ₂ do not adversely affect each other, reducing their amounts can further increase the P ₂ O ₅ concentration in the slag, thereby increasing the effect as a fertilizer. Also, M
If nO can be separated, it can be expected to be effectively used as a Mn source.

The present invention has been made based on the above findings, and the gist is as follows (1) and (2). (1) P-containing slag obtained by removing low-P hot metal having a P concentration of 0.15% or less into a hot metal bath is supplied to a hot metal bath, and a carbon material and iron oxide or / and oxygen are supplied, and P in the slag is supplied. Is reduced and extracted in a hot metal bath to obtain 0.5 to 3% of P and 0.1%.
The following first step of producing hot metal containing Si, and after removing the slag generated in the first step, the slag basicity (CaO / SiO ₂ wt% ratio) of the hot metal after treatment becomes 2 to 8 the flux was added to, more P ₂ O ₅ concentration after treatment by the addition and / or second step be reduced to less than 1% of carbon concentration of oxygen contained in molten pig iron by performing a blowing gas iron oxide source A method for producing high-P slag, wherein a slag of 10 to 30% is obtained.

(2) Mn and Si in the hot metal are reduced by adding iron oxide and / or oxygen to the hot metal produced in the first step described in the above (1), and then described in the above (1). By performing the processing of the second step, P ₂
Process for producing a high P slag O ₅ concentration is characterized by obtaining a slag 10 to 35%.

[0013]

FIG. 1 is a longitudinal sectional view of a converter as a configuration example of a final de-P process. As the reaction vessel for the de-P treatment, a converter 1 which is usually used is suitable, but a means for adding and stirring the de-P flux and the iron ore 8 (FIG. 1 shows an example using the bottom-blown gas 7). Other facilities may be used as long as they have the above. In addition, 2 is a top blowing lance, 3 is a bottom blowing nozzle, 4 is high P content pig iron, 5 is slag 6 is oxygen gas.

According to the present invention, first, the P concentration is 0.15
% Or less of hot metal is prepared as a raw material slag obtained by removing P from the molten iron and put into a low P hot metal bath accommodated in the converter 1, for example. At this time, since the raw material slag is usually in a solid state, it is burned and melted, and a carbon material and iron oxide or / and oxygen are supplied as a raw material for reducing and extracting P in the slag into a hot metal bath.

The carbon material uses coke or pulverized coal as a fuel and a reducing agent, and the iron oxide uses iron such as mill scale or ore as an oxygen supply source of a supporting gas. When the converter 1 is used, oxygen can be easily supplied by using the oxygen blowing upper lance 2.

[0016] The P concentration in the hot metal subjected to the final P removal is 0.5 to
Preferably between 3%.

If the P concentration is less than 0.5%, the P ₂ O ₅ concentration in the slag must be less than about 10%. P
There is not much difference from those with ₂ O ₅ concentration around 5%.

If the P concentration exceeds 3%, the amount of slag required for the de-P treatment becomes excessive, and the slag overflows due to forming and the de-P efficiency decreases due to insufficient stirring power, which is not preferable.

On the other hand, if the P concentration exceeds 3%, P
The reaction driving force when reducing and extracting is reduced, and the reduction time becomes longer, which is not preferable. The slag basicity (CaO / SiO ₂ ) at the time of the final P removal treatment is preferably from 2 to 8.

If the basicity of the slag is less than 2, the P removal ability becomes insufficient, and the P ₂ O ₅ concentration in the slag becomes less than 10%, which is not preferable. If the basicity exceeds 8, the initial melting point of the slag becomes too high, and the molten steel temperature after the final removal of P is 155.
Even if the temperature is 0 ° C. or higher, slag is not sufficiently formed and stable P removal ability cannot be obtained.

A more preferred range of the basicity is from 4 to 8. Quicklime, limestone and the like can be used as a CaO source. S
Silica sand, silica stone, etc. are used as the iO ₂ source.

In addition, it is preferable to use various slags containing at least one of CaO and SiO ₂ , since the amount of slag waste generated from steelworks can be reduced.
CaF ₂ is a component that lowers the melting point of slag.
_Since it reacts with ₂ O ₅ to form apatite and loses its effect as a fertilizer, its content in slag is preferably less than 1%, preferably less than 0.1%.

The flux may be added all at once in the beginning, or may be added separately with stirring. Since P moves into the slag in the form of P ₂ O ₅ , it is necessary to add an iron oxide source such as iron ore, sinter, or scale as an oxidizing agent for P, and / or blow oxygen gas. In the case of an iron oxide source, it may be added at once as in the case of the flux, or may be gradually added while stirring. In the case of oxygen gas, it is desirable to blow in while stirring.

After the addition of the above flux and the like, the inside of the vessel is stirred to perform de-P treatment. The stirring method includes a method of blowing gas from a bottom blowing nozzle and a mechanical stirring method using an impeller. Good or may be used together.

The high basicity slag, because of the high melting point and hardly the temperature of the molten iron bath with the progress of the decarburization reaction is increased slag formation, and slag formation exceeds the melting point of the slag, P ₂ produced by the oxidation of P O ₅ to dissolve. Since P ₂ O ₅ has a function of lowering the melting point of slag, the melting point of the flux in which P ₂ O ₅ is dissolved further lowers, and the dissolution of the surrounding unslagged flux can be promoted. Accordingly, the flux can be quickly turned into slag without adding CaF ₂ .

The reason why the carbon concentration in the molten steel is set to 1.0% or less is that if it exceeds 1.0%, the temperature of the molten steel due to the heat of combustion reaction of carbon becomes insufficient and becomes less than 1550 ° C., and the fluorite becomes 1%. This is because it must be added in excess of. The slag that has become slag has P gradually generated by the oxidation of P.
₂ O ₅ is enriched, and the P concentration in the hot metal decreases. When a certain level is reached, P ₂ O ₅ in the slag and P in the hot metal reach equilibrium, and the de-P reaction stops.

After the completion of the first step, a processing step for removing Mn and Si in the hot metal may be added in order to obtain a higher P slag. In this processing step,
The hot metal is agitated while adding oxygen and / or iron oxide to promote oxidation of Mn and Si. In this case, if the basicity of the slag (CaO / SiO ₂ : weight% ratio of the two components in the slag) is too high, P is also oxidized at the same time, and the P ₂ O ₅ concentration in the slag during the final de-P treatment in the second step is reduced. In order to cause a decrease, the basicity of the slag is desirably 0.5 or less.

As described above, the P ₂ O ₅ concentration is 10 to 35 by adding the de-P flux adjusted so that the slag basicity (CaO / SiO ₂ ) is 2 to 8 to the pretreated hot metal. % Of high P slag can be obtained.

The P ₂ O ₅ concentration in the slag varies depending on the composition of the slag, the initial P concentration in the hot metal, and the like. In the case of the method of the present invention, 10% to 30% in the first aspect and 1% in the second aspect.
0 to 35%. P ₂ O ₅ concentration in the slag in a normal converter refining and molten iron removal P can be increased to 2-6 fold by the method of the present invention because it is approximately 5%.

The high-P slag is separated from the hot metal and discharged out of the reaction vessel. Since the slag has a high P concentration, it can be used not only as a fertilizer but also as a raw material for phosphoric acid. Also,
By further de-P treatment of the molten steel after final de-P,
It is also possible to smelt molten steel having a concentration of 0.02% or less to produce a product.

[0031]

EXAMPLE Using a converter, the P concentration was 0.10 to 0.11.
% Of low-P hot metal as a starting material, the slag generated by removing the hot metal from the hot metal is put into a converter, carbon material and oxygen are supplied and melted, and P in the slag is converted into a hot metal bath. And 2 tons of hot metal containing about 2% P was melted.

To the hot metal, a P-free flux (CaO in quicklime = 92%, T.Fe in iron ore = 65%) shown in Table 1 was added, and the molten iron was treated by changing the oxygen injection amount and the iron ore input amount. The final P was removed by changing the carbon concentration and bath temperature. The method of adding the flux was such that a half amount was initially used, and the remaining was performed 5 minutes after the start of the acid supply.

[0033]

[Table 1]

After the addition of the flux and the iron ore, oxygen gas was blown upward while the bottom was stirred using argon gas to perform a final de-P treatment. Twenty minutes after the start of the acid supply, the final removal of P was completed, and the hot metal and slag were separated and discharged. Final removal P
Table 2 shows the hot metal, the molten steel component, and the slag component before and after the treatment.

[0035]

[Table 2]

In Examples 1 and 2 of the present invention, the P ₂ O ₅ concentration was 18%.
The above high P ₂ O ₅ slag can be easily obtained. In particular, in Example 2 of the present invention in which the amount of slag is 200 kg or less per ton of molten steel, the P ₂ O ₅ concentration of 25% which could not be obtained by the Thomas method.
The above high P slag was obtained.

In addition, as a result of using the high P slag of Examples 1 and 2 of the present invention as a fertilizer, it could be used without any particular problem. In Comparative Example 1 in which the temperature for the de-P treatment was low, fluorite was added such that the CaF ₂ concentration in the slag became 15% in order to ensure the fluidity of the slag after the treatment. As a result, although the P ₂ O ₅ concentration in the slag could be increased, apatite was formed due to the presence of CaF ₂ and could not be used as a fertilizer.

In Comparative Example 2, since the de-P treatment temperature was low and fluorite was not used, the fluidity of the slag was extremely reduced, the de-P reaction did not proceed sufficiently, and the P ₂ O ₅ concentration in the slag was low. Was also less than 10%. In Comparative Example 3, the P concentration in the hot metal before the treatment was as low as 0.1%, and the P ₂ O _{5 in} the slag after the treatment was low.
The concentration was 5% or less, and sufficient performance as a fertilizer could not be obtained.

2 tons of the same hot metal as in Example 1 of the present invention were charged into a converter, and prior to the final de-P treatment, 30 kg of iron ore and 2 kg of quick lime were introduced and oxygen was supplied at a flow rate of 1 Nm ³ / min for 5 minutes. The treatment was performed to remove Mn and Si in the hot metal. Mn and Si before the treatment were 1.4% and 0.06%, respectively, and Mn and Si after the treatment were 0.25% and 0.1%, respectively.
01%. As a result of performing the de-P treatment on the hot metal under the same conditions as in Example 1 of the present invention in Table 1, P ₂ O ₅ in the slag was obtained.
The P ₂ O ₅ concentration was 23%, which was higher than that of Inventive Example 1. As a result of using this high P slag as a fertilizer, it could be used without any problem.

In the converter, 2 tons of the same hot metal as in Example 2 of the present invention were charged into the converter, and prior to the final de-P treatment, 30 kg of iron ore and 2 kg of quicklime were added and oxygen was supplied at a flow rate of 1 Nm ³ / min for 5 minutes. After the treatment, Mn and Si in the hot metal were removed. M before processing
n and Si were 1.3% and 0.05%, respectively, and Mn and Si after the treatment were 0.2% and 0.01%, respectively. This hot metal was removed under the same conditions as in Example 2 of the present invention.
As a result of performing the treatment, the P ₂ O ₅ concentration in the slag was 31%, which was no. Higher slag P ₂ O ₅ concentration than 2 was obtained. As a result of using this high P slag as fertilizer,
It could be used without any problem.

[0041]

According to the present invention, a slag uniformly containing a high concentration of P ₂ O ₅ can be produced from pig iron having a low P content as a starting material. This slag can be used directly as fertilizer.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a final P removal process.

[Explanation of symbols]

 1: converter, 2: top blow lance, 3: bottom blow nozzle, 4: high P content pig, 5: slag, 6: oxygen gas, 7: bottom blow gas (Ar, nitrogen, etc.), 8: de-P flux , Iron ore, etc.

Claims (2)

[Claims] 1. A P-containing slag obtained by removing hot metal having a P concentration of 0.15% or less from a molten iron bath is charged into a hot metal bath, and a carbon material and iron oxide or / and oxygen are supplied to supply P to the slag.
Was reduced and extracted into a hot metal bath to obtain 0.5 to 3% of P and 0.1%.
A first step of producing hot metal containing 1% or less of Si,
After removing the slag generated in the process, a flux is added to the hot metal so that the slag basicity (CaO / SiO ₂ wt% ratio) becomes 2 to 8, and further an iron oxide source is added and / or A high step of obtaining a slag having a P ₂ O ₅ concentration of 10 to 30% by a second step of blowing oxygen gas to reduce the concentration of carbon contained in the hot metal to 1% or less. Slag production method. 2. The second step according to claim 1, wherein Mn and Si in the hot metal are reduced by adding iron oxide and / or oxygen to the hot metal produced in the first step according to claim 1. Characterized in that a slag having a P ₂ O ₅ concentration of 10 to 35% is obtained by carrying out the treatment of high P.
Slag production method.