JPH1171611A - Lime flux for smelting metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the slag-making property by increasing a molten metal stirring effect during a flux injection without adding fluorite, and to generate a versatile slag of excellent quality which contains no fluorine or non-slag lime in the molten condition, is suitable for a phosphatic and potassic fertilizer, and a raw material of cement and a road bed material. SOLUTION: Powder calcium hydroxide is added to lime flux containing powder quick lime. Alternatively, most of lime flux is changed into calcium hydroxide. These stuffs may be of lump shapes as necessary. The calcium hydroxide is fed into the molten metal in a metal smelting furnace, and the calcium hydroxide is decomposed into quick lime large in a specific surface area. Slight steam explosion generated during the decomposition is intentionally induced, the contact of the molten metal and the flux together with a carrier gas is promoted, and the hydroxide flux is reacted with sulfur and phosphoric acid in the molten metal to promote generation of the molten slag.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lime-based flux for metal refining, and more particularly, to slag of metal inclusions supplied to a molten metal in a metal refining furnace and subjecting the molten metal to dephosphorization, desulfurization, desiliconization and the like. The present invention relates to a lime-based flux which promotes the use of slag and promotes the use of generated slag by avoiding a large amount of fluorite which enhances the slagging property of the flux.

[0002]

2. Description of the Related Art In order to reduce impurity elements in steel materials, deoxidation, desulfurization, dephosphorization, desiliconization, and morphological control of inclusions are performed by various methods using slag during smelting of molten metal. Have been done. In order to promote the production of steelmaking slag by reacting with the sulfur content in the molten metal in metal refining,
A soda ash-based flux or a lime-based flux (mainly quicklime CaO) as a slag-making agent is poured into the molten metal in a lump or is blown in a powder form from a sublance.

[0003] When the powdery flux is used, injection is performed together with nitrogen or argon gas in order to enhance the stirring effect of the molten metal. However, the uniform mixing time is shortened as compared with the injection of gas alone, and And slag generation can be promoted. However, the use of soda ash-based flux has recently decreased due to reasons such as the fact that the generated slag cannot be reused, and lime-based flux has rapidly come into the spotlight.

[0004] By the way, the finer the lime-based flux blown from the lance, the higher the reactivity, and for example, a 300 mesh mesh is preferable. Therefore, various studies have been made on the pulverizing method. On the other hand, lime originally has a high melting point (the melting point of CaO is 2,572 ° C.), and in order to promote the formation of reaction slag in the molten metal, the following method can be considered in addition to the above-described fine lime-based flux. ing. The reason for this is to improve the hydration property, leave very little CO ₂ at the center of the lime powder, add fluoride such as fluorite as a soot solvent to lower the melting point, and add 2CaO.SiO around the lime powder. ₍₂ ) not to form a film, and ( ₂ ) to make artificial steel slag.

[0005] The above-mentioned fluorite CaF ₂ is an important raw material for promoting separation of slag and dephosphorization and desulfurization as a solvent that combines with impurities so as to prevent impurities from entering the product in steel making operations and the like. In particular, a large proportion is consumed in steelmaking operations. It is well known that the addition of a fluoride such as fluorite to a lime-based flux has the effect of substantially lowering the melting point of the lime-based flux during slag making. This is because in the dissolution mechanism of CaO in the molten slag, the compound phase 2CaO · SiO ₂ generated in the CaO · SiO ₂ -based slag is easily slagged through the wetting layer generated by the melting of fluorite having a low melting point. It is said.

[0006] The quicklime CaO as the lime-based flux described above is obtained by converting limestone CaCO ₃ from 900 ° C to 1,20 ° C.
It can be made by firing at 0 ° C. (see the part after E in FIG. 3 described later). It has a high compressive strength and is strong against impact, and is easy to handle when transported or put into a furnace.
On the other hand, when limestone is fired, a large amount of carbon dioxide gas is generated, and when firing and burning temperature are high, fuel consumption is increased. Therefore, there is a problem that an increase in grinding energy cannot be avoided.

[0007] Therefore, when a lime-based flux must be produced, it is desired to reduce the consumption of limestone, a natural resource, for which stable supply is not guaranteed forever. Incidentally, a method for producing quicklime powder as a slag-making agent for dephosphorization or desulfurization from limestone is disclosed in Japanese Unexamined Patent Publication No.
No. 9045.

The CaO-based flux for dephosphorization and desulfurization mainly comprises quicklime CaO, magnesia MgO, and dolomite. When dephosphorizing, P ₂ O
_A small amount of gaseous oxygen or iron oxide as an oxygen-increasing material is added in order to form No. ₅ and stabilize its association with CaO in the slag. This is shown by the following equation: 2 P +5 O + n (CaO ) ─ → (nCaO · P 2 O 5) 2 P + 5FeO + n (CaO) ─ → (nCaO · P 2 O
₅ ) + 5Fe The underlined expression in the formula indicates that the compound exists in the molten metal.

Further, as described above, fluorite CaF ₂ is added to promote slag formation. When desulfurizing,
It is mainly composed of CaO, MgO and dolomite, to which carbon C, aluminum ash (containing alumina Al ₂ O ₃ and some metal Al) and CaF ₂ are added. This is shown by the following equation: 3 (CaO) +3 S ─ → 3 (CaS) +3 O 2 Al +3 O ─ → (Al 2 O 3) those underlined in the formula represents that are present in the melt. Incidentally, those described on the right side of each of the above formulas are slags except those underlined.

When the molten metal is deoxidized with Al, a CaO.Al ₂ O ₃ slag is basically produced. This CaO.Al ₂ O ₃ -based slag has a high desulfurization ability and a high deoxidation ability. Therefore, this calcium aluminate has been attracting attention as a flux in the secondary refining of molten metal. In particular, 12CaO · 7Al ₂ O ₃ has a melting point of 1,385 ° C., and promotes lowering the melting point of slag.

However, in any of the above-mentioned methods, slag formation is not sufficiently promoted, resulting in excessive use of flux. Table 1 is an example of the schematic composition of the dephosphorized desulfurized slag collected from the noro field. As can be seen, free lime (free lime) accounts for more than 10%.

[Table 1]

As described above, if unreacted lime remains in the dephosphorized and desulfurized slag, even if a roadbed material is manufactured from this slag, the remaining free lime CaO will be dandruff as time passes and the roadbed material will be used as a roadbed material. There is a drawback that the qualities of the materials are reduced.

Recently, deterioration of concrete structures due to carbonation, salt damage, alkali-silica reaction and the like has also become a problem. Further, sulfur oxides and nitrogen oxides are released into the atmosphere with the burning of petroleum and the like, and when acid rain having a pH of about 4.7 falls, the concrete exposed surface is significantly deteriorated.

On the other hand, when the above-mentioned fluorite is used for accelerating slag formation, fluorine having high reactivity for forming compounds with all elements except the inert gas remains in the slag. Therefore, despite the presence of phosphorus, it cannot be used as a fertilizer due to the presence of fluorine, and is often forced to be dumped in a landfill or the like.

[0015]

The quicklime used in the flux is calcium hydroxide Ca (OH) _2.
Can also be produced by dehydration. When calcium hydroxide is dehydrated, it is extremely reactive when it is dehydrated, because the specific surface area is large (see the portion after D in FIG. 3 described later). According to this production method, there is an advantage that quick lime can be obtained at a lower temperature than when calcining limestone. This is supported by the fact that the temperature of the portion D in FIG. According to this figure, it can be seen that the specific surface area of the former is several steps larger than that of the latter.

[0016] However, empirical studies have not been conducted on whether or not it can be used as a powdery flux in metal refining.
This is because there is a concern that steam explosion may occur due to the OH group of calcium hydroxide, and conversion to lime-based flux has hardly been attempted. Another reason is that calcium hydroxide is a fine powder and is difficult to handle when calcined. It is also difficult to solidify as a mass flux when calcined. doing.

Japanese Patent Application Laid-Open No. H6-157085 discloses that 5% by weight of CaO ground to calcium hydroxide is used.
It describes a method of producing granulated quicklime for metal refining by mixing and granulating the resulting mixture by mixing with 40 to 40% by weight. Japanese Patent Application Laid-Open No. 7-62420 discloses that aluminum hydroxide powder is 70% by weight to 20% by weight, and 30% by weight to 80% by weight of calcium hydroxide powder is mixed and granulated. A method for producing a lime-based flux for metal refining by calcining is described.

In any of the lime-based fluxes, calcium hydroxide is mixed into quicklime to suppress the consumption of limestone, which is a natural resource, by utilizing calcium hydroxide, and to reduce the generation of carbon dioxide during production. And contribute to environmental conservation. In addition, compared with the method for producing a lump of lime-based flux in which limestone is used as a main raw material, it is possible to perform calcination at 700 ° C. to 1,000 ° C., which is low.
In addition to reducing the fuel consumption rate, the energy consumption can be reduced because the pulverizing step and the like, which consume a lot of power, are reduced.

Further, when producing a lime-based flux having a low melting point in order to improve slagging properties by adding fluorite, the reaction of fluorite is suppressed and damage to the fire-resistant wall of the firing furnace is reduced as much as possible. Thus, an increase in the firing temperature can be suppressed, fuel consumption can be reduced, and an inexpensive lime-based flux can be obtained.

However, in any of the examples described in the above-mentioned publications, 5 to 20 mm is obtained by calcining almost all of the calcium hydroxide by calcining.
It is granular. Even when the molten metal is injected into the molten metal by crushing or the like, it often floats immediately on the molten metal surface as fine particles blown, although the molten gas has an effect of stirring the molten metal by the carrier gas. Therefore, direct contact in the molten metal is small, and most of the slagging action tends to proceed only near the molten metal surface. As a result, there is a disadvantage that the dephosphorization and desulfurization are not sufficiently achieved or the slagification has to be advanced over a long time.

FIG. 3 shows the “Journal of
Applied Chemistry '(Journal of Applied Chemistry), page 794, issued on December 8, 1958, "Fig. 5 showing" samples of calcium hydroxide and calcium carbonate heated at various temperatures for 5 hours ".
1 (b) is transcribed.

This indicates a change in the specific surface area (m ² / g) that occurs with respect to the temperature heated in the atmosphere. The portion A is in the state of Ca (OH) ₂ , and the portion after D is Ca (OH) _2.
(OH) ₂ decomposed into CaO, B
Is in the state of CaCO ₃ , and the part after E is Ca
It indicates that CO _{3 is changed} to CaO.

As can be seen from the above, the above-mentioned Japanese Patent Application Laid-Open
In the techniques disclosed in JP-A-157085 and JP-A-7-62420, calcium hydroxide constituting a part of the flux is calcined at 700 ° C. to 1,000 ° C., so that CaCO ₃ is calcined. As in the case of baking, it is baked and its specific surface area is as low as 13 m ² / g or less.

Even when viewed from FIG. 3, the maximum specific surface area cannot be obtained when calcining is performed, so that the slagging property is lowered. This is to increase the compressive strength as described above so that handling can be facilitated.

In addition, Ca (O
When H) ₂ remains, Ca (OH) ₂ → Ca
H ₂ O by the reaction of O + H ₂ O is produced, depending on the intention to avoid the steam explosion based thereon. In addition, H ₂
If O is decomposed and hydrogen is mixed with the molten metal, there is a risk that hydrogen embrittlement may occur in steel products and the like as products.

The present invention has been made in view of the above problems, and its object is to reduce the consumption of limestone, which is a natural resource, while utilizing calcium hydroxide, and to reduce the consumption of carbon dioxide gas during production. Reduce the generation of lime-based flux, minimize energy consumption by minimizing the burning process and the crushing process that consumes a lot of power, and significantly reduce production costs. Further, it is an object of the present invention to enhance the agitation action of molten metal at the time of flux injection without adding fluorite to improve slagging properties.

In addition, the molten slag contains no fluorine and can produce high quality slag which can be used as a cement raw material, phosphoric acid, potash fertilizer, etc., opens up the use of industrial waste, and is a natural resource. An object of the present invention is to provide a lime-based flux for metal refining that has achieved a reduction in limestone consumption.

It is to be noted that it is desirable that the flux for the slagging action be porous, that is, have a large specific surface area, as described above. Phosphorus or sulfur enters each pore of the porous flux. This is because the dephosphorization and desulfurization reaction is promoted. Therefore, as can be seen from FIG. 3, when CaO having a large specific surface area, which has just been generated from calcium hydroxide, is used as a flux, the slagging reactivity becomes extremely excellent, and the decomposition of Ca (OH) ₂ results. Water vapor explosion in the molten metal can be avoided depending on the supply method to the molten metal, and even if it is mixed with hydrogen in the molten metal, it has reached the technical level where hydrogen can be completely removed in the subsequent refining operation. The present invention has been made based on such findings.

[0029]

SUMMARY OF THE INVENTION The present invention relates to a lime-based system which is supplied to a molten metal in a metal refining furnace and is used to react with sulfur or phosphoric acid in the molten metal to promote the production of molten slag. Applies to flux. The feature is that lime-based flux is converted into powdered calcium hydroxide Ca
(OH) ₂ .

The powdered lime-based flux may be mixed with powdered quick lime CaO. Any of the fluxes may contain fluorite, aluminum ash, dolomite, carbon, potassium mineral or MgO, or may be mixed with fine powder scale or iron oxide.

As the lime-based flux, powdered calcium hydroxide Ca (OH) ₂ is formed into granules or agglomerates, which are not calcined.

The granulated flux may be mixed with powdered quicklime CaO before granulation. Any of the fluxes may contain fluorite, aluminum ash, dolomite, carbon, potassium mineral or MgO, or may be mixed with fine powder scale or iron oxide.

The granulated flux is preferably cured naturally after granulation or soft-baked after granulation.

Regarding the lime-based flux, carbide slag can also be used as calcium hydroxide, regardless of whether it is powdery or granulated.

[0035]

According to the present invention, calcium hydroxide can be applied to lime-based flux as a main raw material without burning. There is no energy consumption for calcining the calcium hydroxide, and high-activity quicklime having a large specific surface area can be automatically obtained by the heat of the molten metal. Since the amount of quicklime used can be suppressed, not only can the energy consumption for firing CaCO ₃ be reduced, but also the amount of carbon dioxide gas generated from the raw material during firing is reduced.

When the lime-based flux is injected into the molten metal, the fine calcium hydroxide which has reached about 500 ° C. due to the heat of the molten metal becomes activated lime having a large specific surface area, and its slagging property is remarkably improved. In addition, water vapor generated from calcium hydroxide in the molten metal induces a slight explosion, which enhances the agitation action of the molten metal by the carrier gas and improves the dispersibility of the lime-based flux.
This also improves the contact efficiency between the molten metal and the flux during refining and promotes the dephosphorization and desulfurization action. Therefore, slag with less free lime is generated, and the form of inclusions in the molten metal can be controlled so as to reduce impurity elements in the metal material.

The same applies to the case where the powdered lime CaO is mixed with the powdered lime-based flux. If any of the fluxes contains fluorite, aluminum ash, dolomite, carbon, potassium mineral or MgO, the desulfurization action can be enhanced. Inclusion of fine powder scale or iron oxide can enhance the dephosphorization effect.

As the lime-based flux, powdered calcium hydroxide Ca (OH) ₂ may be granulated or agglomerated, and even if this is not calcined, the same slagging as the powdery flux is performed. In addition to being able to exhibit the property, the handling property is improved due to the materialization.

The above-mentioned granulated flux may be premixed with powdered quicklime CaO before granulation, or may contain fluorite, aluminum ash, dolomite, carbon, potassium mineral or MgO, or may have a fine powder scale or If iron oxide is added, desulfurization and dephosphorization can be exerted.

If the granulated flux is naturally cured after granulation, CaCO ₃ is formed on the surface of the granulated product, and if softened after granulation, CaO is generated on the surface, resulting in high shape retention. Become.

When carbide slag is used as calcium hydroxide, the use of industrial waste is opened, and natural resources can be effectively used and resources can be recycled. Further, resource saving is achieved by suppressing the consumption of limestone, and the amount of carbon dioxide gas generated from limestone during firing is reduced, which also contributes to environmental conservation.

When any of the lime-based fluxes is used for metal refining, the resulting slag can be used as a raw material to obtain high-quality cement or phosphoric acid / potassium fertilizer, and can be used as a roadbed material. Since the lime-based flux according to the present invention reduces the free lime as much as possible, even if the generated slag is used as a cement raw material, it is a dephosphorized desulfurized slag cement excellent in alkali silica reactivity and acid resistance. can do. Since unreacted lime does not remain as much as possible as the roadbed material, the roadbed material is chemically stable. In addition, since lime-based flux does not contain fluorite in principle, it is unlikely that highly reactive fluorine will remain in the slag, and if slag is used as phosphoric acid / potassium fertilizer, it is harmful. Does not elute.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a lime-based flux for metal refining according to the present invention will be described in detail. This lime-based flux is supplied to the molten metal in a metal smelting furnace such as a converter or an electric furnace, or to the molten metal received in a torpedo car or a ladle, etc., in order to promote the generation of molten slag to reduce impurity elements in the molten metal. Used for That is, during the refining of the molten metal, lime-based flux is injected into the molten metal as an auxiliary material,
It reacts with sulfur, phosphoric acid, silicic acid, and the like in the molten metal to promote the production of metal slag, and can also control the form of inclusions.

The lime-based flux is powdered lime Ca
It is obtained by adding fine powder of calcium hydroxide Ca (OH) ₂ to a lime-based flux containing O. The content of calcium hydroxide may be arbitrarily set, but is desirably set to 3% by weight (hereinafter referred to as%) or more. Needless to say, it is preferable to increase the content of Ca (OH) ₂ , and it is also possible that the content of Ca (OH) ₂ is extremely high or nearly 100%, that is, calcium hydroxide alone.

Quick lime CaO is approximately 90% of limestone CaCO _3.
It is made by baking at 0 ° C. Although the generation of carbon dioxide CO ₂ is inevitable that time, since it is mixed with calcium hydroxide when used as lime-based flux consumption CaO is less, the generation of carbon dioxide gas during production is suppressed environmental Also contributes. Voids exist where the carbon dioxide gas escapes, the specific surface area of the flux increases, and the flux reacts with the sulfur component in the molten metal and becomes highly active in producing slag.

Although this CaO has high compressive strength and is strong against impact, it needs to be pulverized to obtain a powdery flux. Power consumption is inevitable for the crushing,
As described above, the consumption amount is small and the increase in the pulverization energy is also avoided.

On the other hand, calcium hydroxide is lime (quick lime C).
It is produced by adding water to aO). Alcohol with water can be used instead of H ₂ O to make Ca (OH) ₂ . These are very fine particles and have a small specific surface area. In addition, you may implement | achieve in the form which hydrated dolomite as Ca (OH) ₂ . In this case, Mg (O
H) _{2 is} also contained at the same time, which is convenient for the purpose of desulfurization as described later. Of course, commercially available slaked lime may be used as calcium hydroxide,
Carbide slag may be used instead of calcium hydroxide. This is because carbide slag contains 90% or more of Ca (OH) ₂ , and in many cases, 96%.

The carbide slag is made of carbide CaC ₂
A large amount is generated when acetylene gas C ₂ H ₂ is produced by adding water to water. This produces 1.16 tons of carbide when one ton of carbide is produced, and in Japan, more than 500,000 tons of waste must be disposed or reused annually.
ADVANTAGE OF THE INVENTION According to this invention, the way of utilization of industrial waste is also opened, and effective utilization of natural resources and recycling of resources are attained. Thus, limestone as a raw material and discarded from other industrial fields can be used for the production of slag-making agents for steelmaking and the like.

As the lime-based flux, the above-mentioned Ca
In some cases, it is only necessary to use a mixture of O and Ca (OH) ₂ or only Ca (OH) ₂ . However, when the main purpose is dephosphorization, iron oxide or fine powder scale,
It is preferable to mix Fe (OH) ₂ , Al (OH) ₃ or gaseous oxygen.

For the purpose of desulfurization (deoxidation), metals such as metal Mg, MgO, Mg (OH) ₂ or dolomite, carbon C, potassium minerals such as K ₂ CO ₃ and KCl, and aluminum ash (Al ₂ O 3) ₃ + metal Al) and fluorite are preferably mixed in a little. These are acceptable as long as they do not adversely affect the quality of the flux, and it is needless to say that they do not impair the quality of processed products such as fertilizers manufactured from dephosphorized and desulfurized slag. .

When such a lime-based flux is blown into the molten metal via a sublance or the like by a flux injection method, the powder mixture is transferred in a supply pipe along with argon or nitrogen gas as a carrier gas. In this case, it is necessary that the main component quicklime and calcium hydroxide are uniformly mixed so that the components are not biased when injected into the molten metal.

Considering that the powder flux is transported in a pipe or a lance by air, about 1% of stearic acid or silicone oil is added. When the mixing ratio of calcium hydroxide is 50% or more, 2% to 3% is added. If the amount is increased to about%, the action of lowering the angle of repose makes it possible to transport the mixed powder uniformly in the pipe.

Further, even in the molten metal, the flux is evenly diffused, and the slag property is improved. Since this stearic acid has the property of preventing moisture, CaO
You can also keep the dandruff off. Incidentally, the addition of stearic acid or silicon oil does not adversely affect the steel quality.

The powdered lime-based flux blown into the molten metal tends to float immediately, but calcium hydroxide having a melting point of 580 ° C. comes into contact with the high-temperature molten metal and immediately comes into contact with the molten metal.
℃, Ca (OH) ₂ ─ → CaO + H ₂
CaO is produced by the reaction of O 2, or the following reaction is caused by the carbon content in the molten metal. C + Ca
(OH) ₂ ─ → CaO + CO ₂ + H ₂

This is an endothermic reaction, which lowers the temperature of the surroundings, so that heating of the generated CaO is suppressed. Accordingly, the densification (recrystallization) of CaO does not proceed rapidly, and as can be seen from FIG. 3, the specific surface area is larger than that of quicklime changed from limestone CaCO ₃ , which is 30 to ² times or three times that of quicklime. g and become highly reactive (see FIG. 3).

It should be noted that the generation of quicklime from calcium hydroxide occurs simultaneously with the above two reactions, so that the generation of a large amount of H ₂ O is suppressed. About 10 kg of flux is used per ton of steel.
If the injection is performed little by little over a period of 30 minutes to 30 minutes, a severe steam explosion due to the high heat of the molten metal does not occur.

Activated lime CaO generated by decomposition from Ca (OH) ₂ reacts with C and S in the molten metal as follows. _{CaO + H 2 O + C +} S ─ → CaS + CO 2 + H 2 Although CO ₂ gas and H ₂ gas as can be seen from this reaction occurs, it facilitates stirring of the molten metal CO ₂ gas is bubbled acts together with a carrier gas, hydroxide The small amount of water vapor generated when calcium is decomposed induces a small-scale explosion, which promotes stirring of the molten metal and dispersion of the flux, and further promotes the reactivity during floating in the molten metal to further enhance the slagging action. It is noteworthy in the present invention that the improvement is achieved. Needless to say, such a phenomenon becomes more remarkable when coke powder is added to the lime-based flux as described above.

Injection of CaO powder using a lance or the like has been conventionally performed. However, since the dispersibility after blowing is low, the reaction concentrates near the lance, and the lance may be vibrated. . However, it has been confirmed that the lime-based flux according to the present invention improves the flow of the molten metal and the diffusivity of the flux due to the gas agitation for the reasons described above, and as a result, the vibration of the lance is suppressed as much as possible.

Incidentally, hydrogen generated by decomposition of generated H ₂ O may be mixed with the molten metal. But,
With the current technology, hydrogen can be completely removed from the molten metal in a subsequent vacuum degassing process (for example, RH method), so that the quality of the steel material is not affected at all.

Not only CaO naturally generated from calcium hydroxide using the heat energy of the molten metal, but also CaO introduced together with Ca (OH) ₂ ,
High slagging property is exhibited while floating in the molten metal and on the surface of the molten metal. In other words, without the need to actively add fluorite to lower the melting temperature of slag generated during refining, the slagging property is improved by a flux with a large specific surface area, and the addition of lime-based flux that is usually added The form of the inclusions in the molten metal can also be controlled so that the impurity elements in the steel material are reduced while reducing the amount. As a result, the molten slag contains almost no unreacted lime or fluorine, and produces high-quality slag that can be used as a raw material for cement, phosphoric acid, potassium fertilizer, and the like, and is also used as a roadbed material.

The lime-based flux used for a steelmaking furnace such as a converter and an electric furnace has been described above as an example. The main lime-based flux is C
a mixture of aO and Ca (OH) ₂ or Ca (OH) ₂
As described above, other auxiliary materials such as alumina, silicic acid, iron oxide and the like can be contained therein.

Next, Ca (OH) ₂ plain or CaO
Granulated lime-based flux containing. Powdered calcium hydroxide Ca (OH) ₂ is mixed with a small amount of water and granulated with a pelletizer or the like, or formed into a bulk using a briquette machine. The size is about 1 mm to 50 mm in diameter, and may be any desired one. Such granules or agglomerates are not burned unlike the prior art described in the section of the prior art.

This is because, as described above, even if calcium hydroxide is introduced into the molten metal, H ₂ O is not generated to such an extent that two reactions in parallel cause severe steam explosion. As described above, the specific surface area is 5 m ² / g or less, and the slag property is inferior.

The purpose of the granulation is to improve the handling property in transporting, charging in a furnace, etc., as compared with powder. The powdered lime-based flux described above spreads randomly on the surface when poured directly into the molten metal, and is taken out of the furnace with the exhaust gas, so it can be used only by injection using a lance etc. Become. On the other hand, if it is granulated, it can be poured into the molten metal from the furnace or can be poured together with the molten metal in ladle refining and the like.

Of course, powdered quicklime CaO may be mixed before granulation, instead of using calcium hydroxide alone. Then, as in the case of the powdery lime-based flux, fluorite, aluminum ash, dolomite, carbon, potassium mineral, or MgO is included, or fine powder scale or iron oxide is added. All are powdered and mixed before granulation. The functions and effects of these are not different from the above-described case.

When the granulation is carried out as described above, it is preferable to carry out natural curing thereafter. As a result, Ca (OH) _{2 on the} surface of the granulated material reacts with CO ₂ in the air, and CaCO ₃
A slightly hard film is formed. Therefore, the shape retention of the granulated material is increased, and the handling is further facilitated.

Instead of this natural curing, soft baking may be performed. In this case, a CaO film is formed on the surface of the granulated material, and the shape retention is improved as compared with the case of natural curing. In the case of soft baking, the granulated product may be dried at about 110 ° C., put into a rotary kiln, and heated at 100 ° C. to 300 ° C.

The fact that carbide slag may be employed as calcium hydroxide is no different from the case of powdery flux. The same applies to the production of cement and phosphoric acid / potassium fertilizer using the slag obtained by using the granulated flux as a raw material, or the roadbed material as it is.

As can be seen from the above description, calcium hydroxide can be applied to lime-based flux as a main raw material without burning. The calcining energy of calcium hydroxide is not necessary, and high-activity quicklime having a large specific surface area can be automatically obtained when it is blown or poured into a molten metal. As a result, the amount of quicklime used can be suppressed, so that not only can the energy consumption for calcining limestone to obtain quicklime be reduced, but also the amount of carbon dioxide generated from the raw material during calcining is reduced.

The unreacted lime is reduced as much as possible as a result of the improved slagging property, and the residual amount of free lime is significantly reduced. Therefore, the lime-based flux according to the present invention is used as a cement raw material. Even if dephosphorized desulfurization slag is employed, it is possible to produce a dephosphorized desulfurized slag cement equivalent to or superior to blast furnace cement excellent in alkali silica reactivity and acid resistance.

As described above, the dephosphorized desulfurized slag produced by using the lime-based flux according to the present invention has a small amount of free lime. There will be no qualitative change, and it will be possible to supply chemically stable roadbed materials. The dephosphorized desulfurized slag may be used as a roadbed material as it is, or may be mixed with some auxiliary materials by a known method. There is no particular problem even if molding is performed for blocking.

On the other hand, by improving the reactivity with calcium hydroxide, a large amount of fluorite is not intentionally added for the purpose of lowering the melting point of the slag, so that the dephosphorized and desulfurized slag contains as little fluorine as possible. When this is used as a raw material to produce fertilizer, it does not contain fluorine, so that it can be provided as a safe and high-quality phosphoric acid / potassium fertilizer.

[0073]

EXAMPLE A molten metal was put into a crucible placed in a high-frequency furnace or covered with a graphite heating element, and Ca (OH) ₂ was added to CaO.
Shows the test results of injection by mixing an appropriate amount. In addition, each flux is conveyed in the pipe by argon gas and supplied to the lower part of the molten metal. Tables 2 and 3 show CaO alone, CaO and C
It shows the residual amount of sulfur and the desulfurization rate in the melt obtained with respect to the mixing ratio of a (OH) ₂ to 2%, 5%, 20%, 50% and the flux of Ca (OH) ₂ alone.

[Table 2]

[Table 3]

Of the results in Tables 2 and 3, FIG. 1 shows the amount of sulfur remaining with time in the molten metal at the middle stage, and FIG. 2 shows the desulfurization rate. According to these, Ca (OH) ₂
If the ratio increases, the amount of sulfur remaining in the molten metal decreases,
It can be seen that the desulfurization rate changes remarkably over time. When calcium hydroxide is used in a large amount as a lime-based flux, as described above, the improvement in reactivity due to its larger specific surface area than CaO was confirmed in the above test, and in addition, small steam explosion generated during decomposition of Ca (OH) ₂ It was also confirmed that the slagging reaction was enhanced based on the improvement of the stirring effect and the dispersion effect.

[Brief description of the drawings]

FIG. 1 is a graph showing the transition of the sulfur content in molten steel due to the progress of slagging over time of a lime-based flux obtained by changing the mixing ratio of quicklime and calcium hydroxide.

FIG. 2 is a graph showing a change in a desulfurization rate due to progress of slagging of a lime-based flux obtained by changing a mixing ratio of quicklime and calcium hydroxide over time.

FIG. 3 is a graph showing the specific surface area of calcium hydroxide and calcium carbonate samples heated at various temperatures for 5 hours.

Claims (11)

[Claims] 1. A lime-based flux which is supplied to a molten metal in a metal refining furnace and used to promote the generation of molten slag by reacting with a sulfur component or a phosphoric acid component in a molten metal, wherein the lime-based flux is , Powdered calcium hydroxide Ca
(OH) ₂ A lime-based flux for metal refining, characterized by being (OH) ₂ . 2. A lime-based flux for metal refining, wherein powdered quicklime CaO is mixed with the lime-based flux described in claim 1. 3. A lime-based flux for metal refining, characterized in that the lime-based flux according to claim 1 or 2 contains fluorite, aluminum ash, dolomite, carbon, potassium mineral or MgO. flux. 4. A lime-based flux for metal refining, wherein the lime-based flux according to claim 1 or 2 contains fine powder scale or iron oxide. 5. A lime-based flux which is supplied to a molten metal in a metal refining furnace and used to promote the production of molten slag by reacting with a sulfur component or a phosphoric acid component in the molten metal, wherein the lime-based flux is , Powdered calcium hydroxide Ca
(OH) ₂ in the form of granules or agglomerates,
A lime-based flux for metal refining, wherein the granules are not burned. 6. A lime-based flux for metal refining, wherein the lime-based flux according to claim 5 is mixed with powdered quicklime CaO before granulation. 7. A lime for metal refining, characterized in that the lime-based flux according to claim 5 or 6 contains fluorite, aluminum ash, dolomite, carbon, potassium mineral or MgO. System flux. 8. A lime-based flux for metal refining, wherein the lime-based flux described in claim 5 or 6 contains fine powder scale or iron oxide. 9. A lime-based flux for metal refining, wherein the granulated flux according to any one of claims 5 to 8 is naturally cured after granulation. 10. A lime-based flux for metal refining, wherein the granulated flux described in any one of claims 5 to 8 is soft-fired after granulation. 11. The method according to claim 1, wherein the calcium hydroxide is a carbide slag.
A lime-based flux for metal refining according to any one of the above.