JP2019151535A - Method of producing phosphate slag fertilizer - Google Patents

Abstract

To provide a method of producing a phosphate slag fertilizer, the method including producing high phosphorous molten iron by reducing steel slag and then producing high phosphorous slag by performing dephosphorylation treatment to the high phosphorous molten iron; not needing to use a converter as a dephosphorylation treatment furnace; securing enough heat source through the dephosphorylation treatment; increasing a degree of freedom of slag composition; and lowering viscosity of the slag.SOLUTION: A method of producing phosphate slag fertilizer of this invention uses a common electric furnace 1 including an arc heater 3 to a reduction treatment furnace that performs reduction treatment 31 to steel slag 13 and to a dephosphorylation treatment furnace that performs dephosphorylation treatment 32. Therefore, the method does not need to use a converter as a dephosphorylation treatment furnace and secures enough heat source through the dephosphorylation treatment to increase a degree of freedom of slag composition and to lower viscosity of the slag.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing phosphate slag fertilizer, in which high phosphate slag is produced using steelmaking slag as a raw material.

Iron ore, which is a raw material for iron making, contains phosphoric acid (P ₂ O ₅ ), and pig iron produced by the blast furnace method contains about 0.1% phosphorus. On the other hand, generally, the lower the phosphorus content in the steel, the better the quality of the steel is obtained. Therefore, dephosphorization is performed in the steel making process for refining the hot metal. In the dephosphorization, slag for dephosphorization is formed on the hot metal surface, phosphorus in the hot metal is oxidized by oxidative refining and transferred to the slag, and the phosphorus concentration in the molten steel after the refining is reduced. The slag collected after refining (hereinafter referred to as “steel slag”) contains about 2% of phosphoric acid transferred to the slag by dephosphorization. Steelmaking slag discharged out of the system is used as civil engineering materials such as roadbed materials or used for reclamation of the ocean, and phosphoric acid contained in the steelmaking slag is not effectively used.

  The problem of uneven distribution of phosphorus resources, depletion of resources, and deterioration of quality in the world has been raised. It is said that the total amount of phosphorus contained in steelmaking slag is comparable to the amount of phosphorus contained in Japanese imported phosphorus ore, and the effective use of phosphorus contained in steelmaking slag has become an urgent issue.

A method is known in which decarburization and dephosphorization refining is performed in a basic converter called a Thomas converter using a high phosphorus hot metal having a phosphorus concentration of about 2% manufactured using high phosphorus iron ore as a raw material. The steelmaking slag formed by the refining method contains a high concentration of phosphoric acid (P ₂ O ₅ ) concentration of 15% or more. When used as a fertilizer, a high fertilizer effect can be obtained. It is known by the name of manure. However, using high phosphorus hot metal, such as that used in the Thomas Converter, and containing a high concentration of phosphoric acid in the steelmaking slag after refining, the currently required phosphorus concentration is, for example, about 0.015% It is difficult to carry out dephosphorization to the product phosphorus concentration level. In addition, high phosphorus iron ore is not used as a raw material for steelmaking at present, and refining using high phosphorus hot metal is not performed.

  As described above, in the blast furnace-converter method currently widely used, the phosphorus concentration in pig iron produced by the blast furnace method is about 0.1%, and in the steelmaking slag in the converter method for refining the molten iron The concentration of phosphoric acid is around 2%. Further, the steelmaking slag contains iron oxide. The phosphoric acid content in this steelmaking slag is considered as a useful phosphate fertilizer resource. The phosphoric acid content in steelmaking slag is concentrated to slag with a high phosphoric acid concentration (hereinafter referred to as “high phosphoric acid slag”). Attempts have been made to use the slag as phosphate slag fertilizer.

In Non-Patent Document 1, as a method for producing phosphoric acid fertilizer from steelmaking slag, after reducing steelmaking slag with an electric furnace, the high phosphorus hot metal is dephosphorized with a Kaldo furnace (converter) and high phosphate slag is produced. A method is shown in which metal is used as molten steel after manufacturing and using high phosphate slag as phosphate fertilizer. In Patent Document 1, P ₂ O ₅ contained in de-P slag is reduced several times to concentrate P in hot metal to about 1 to 3%, and hot metal de-P is performed again with a small amount of slag. A method for obtaining high phosphate slag has been proposed.

Patent Document 2 discloses a high P hot metal (P: 0.5 to 3% by mass, C: around 4.5% by mass, Si: around 0.05% by mass) obtained by reducing and melting steelmaking slag. In a converter, a flux having a basicity of 2 to 8 is added, an iron oxide source is added, or oxygen is blown in to remove phosphorus (temperature after treatment: 1550 ° C. or higher), and molten steel (C: 1 A method for producing mass% or less, P: 0.1 to 0.2 mass%) and slag (basicity: 5 to 6, P ₂ O ₅ concentration: 10 to 30 mass%) is described. Both reduction treatment and dephosphorization refining use a converter as a refining furnace.

  In Patent Documents 3 and 4, oxygen gas is projected together with powdered CaO onto high P hot metal (P: 0.5 to 3 mass%) obtained by reducing and melting steelmaking slag, and the basicity of slag is set to 1. A method is described in which the phosphoric acid concentration is increased to 15% by mass or more by adjusting to 5 or more, and the high phosphate slag is used as a phosphate slag fertilizer. Examples of the reduction furnace include a rotary kiln and an arc furnace, and examples of a dephosphorization furnace include a converter type reaction vessel.

  As described above, various methods have been proposed in which steelmaking slag is reduced to produce high phosphorus hot metal, and then high phosphoric acid slag is produced by subjecting the high phosphorus hot iron to dephosphorization to produce high phosphate slag. . Here, the dephosphorization treatment of the high phosphorus hot metal is oxidation refining, and a converter type refining vessel is used and oxygen gas is used as an oxidation source. In the dephosphorization of high phosphorus hot metal, the dephosphorization load is large, so the basic unit of dephosphorization slag (high phosphoric acid slag) is 100 kg / T or more, and slag forms during dephosphorization using oxygen gas. Therefore, a reaction vessel with a large free board like a converter is required. In addition, the heat source required for dephosphorization of high phosphorus hot metal is covered by the heat of oxidation when oxidizing metals such as C, P, Si, and Fe. Therefore, C in the molten iron is almost oxidized to form molten steel. The temperature rises due to the melting point rise.

  Patent Document 5 describes a method in which the dephosphorization step is performed in multiple stages in order to reduce the amount of slag used during one dephosphorization. Although it is effective that dephosphorization can be performed even in small-scale containers, when multiple dephosphorization processes are performed, there is an increase in heat loss due to an increase in total processing time and multiple slag discharge processes, and the need for an external heat source Increase. In addition, the method of recycling the final dephosphorization slag to the dephosphorization process in the previous stage is effective from the viewpoint of flux reduction, but has a difficulty in handling.

  In Patent Document 6, for a hot metal having a phosphorus concentration of 1% or more, a refining agent melted by a melt projection type fuel burner is added to the hot metal surface, and oxygen gas is supplied to the hot metal surface from an upper blowing lance. A method and an apparatus for manufacturing a phosphate fertilizer that perform dephosphorization are disclosed. The refining agent is dephosphorization refining flux or dephosphorization refining flux and iron oxide, and the hot metal surface slag after dephosphorization refining is used as a phosphate fertilizer raw material.

JP 7-316621 A JP-A-11-158526 JP, 2015-140473, A JP2015-140294A JP 2017-125244 A JP 2017-128747 A

Toshio Onoe Journal of the Japan Institute of Metals, Vol. 19, No. 10 (1980), p. 752

  In a conventional method of reducing steelmaking slag to produce high phosphorus hot metal, and then subjecting the high phosphorus hot iron to dephosphorization to produce high phosphoric acid slag to obtain phosphate fertilizer, a rotary kiln is used as the reduction furnace. In addition to using an arc furnace, a converter reactor is used as a dephosphorization furnace. Therefore, it is necessary to provide a converter-type dephosphorization treatment furnace separately from the reduction treatment furnace, which increases the burden of equipment costs and cannot manufacture the phosphate slag raw material at a low cost.

  Further, in the conventional method described above, the heat source required for the dephosphorization treatment of the high phosphorus hot metal is heated by burning C, P, Si in molten iron with oxygen gas blown into the furnace. Therefore, when [C] is low in the initial molten iron or when [C] is desired to remain after dephosphorization, the heat source cannot be secured sufficiently, and the temperature rise of the molten iron and slag becomes insufficient, resulting in a slag composition. A slag composition with a high melting point could not be used, and the slag viscosity could not be lowered sufficiently.

  The present invention reduces steelmaking slag to produce high phosphorus hot metal, and then dephosphorizes the high phosphorus hot iron to produce high phosphoric acid slag, which is used as a phosphoric acid slag fertilizer as a dephosphorizing furnace. To provide a method for producing phosphoric acid slag fertilizer that does not require a converter and that can secure a sufficient heat source by dephosphorization treatment to increase the degree of freedom of slag composition and to reduce the viscosity of slag. With the goal.

That is, the gist of the present invention is as follows.
(1) Steelmaking slag containing phosphoric acid and iron oxide and charcoal are charged into an electric furnace, arc heating is performed, and steelmaking slag is reduced by the charged charcoal and reduced slag (reduced slag) Is called "unit reduction treatment"
The molten iron generated or increased by performing the unit reduction treatment once or a plurality of times is stored in the electric furnace as it is, or once discharged from the electric furnace and then charged again in the same electric furnace,
Phosphorus characterized in that a high-phosphate slag having a P ₂ O ₅ concentration of 10% by mass or more is produced by introducing a CaO source and an oxygen source into an electric furnace and performing arc heating to dephosphorize the molten iron. Method for producing acid slag fertilizer.
(2) The CaO source charged into the electric furnace in the dephosphorization treatment is one or more of molten steelmaking slag, steelmaking slag powder, quick lime powder, limestone powder, dolomite powder,
The method for producing phosphate slag fertilizer according to (1) above, wherein the oxygen source is one or more of iron ore powder, dust powder, and scale powder.
(3) In the dephosphorization process, gas is introduced by lance insertion, or a variable flow rate gas injection tuyere or nozzle is provided at the bottom or wall of the electric furnace to introduce gas into the iron bath, and the iron bath is stirred. The manufacturing method of the phosphate slag fertilizer as described in said (1) or (2) characterized by performing.
(4) A part or all of the molten iron generated or increased by performing the unit reduction treatment once or a plurality of times is once discharged from the electric furnace to another container,
In the presence of slag having a mass ratio of (CaO) / (SiO ₂ ) of 1.5 or less, an oxygen source is introduced into the molten iron in the separate container to reduce the [Cr] concentration in the molten iron to 0.1 mass% or less. The method for producing phosphate slag fertilizer according to any one of (1) to (3), wherein the molten iron is reduced and charged in the same electric furnace again.
(5) Discharge the high phosphoric acid slag from the electric furnace, and further add quick lime or limestone and iron oxide into the electric furnace to reduce the [P] concentration in the molten iron to 0.15% by mass or less (hereinafter “ After finishing the dephosphorization process ”), the molten iron is discharged and used as a raw material for steelmaking, and the following reduction treatment is started while leaving the slag and molten iron remaining in the furnace. The manufacturing method of the phosphate slag fertilizer as described in any one of said (1) to (4).

  The present invention reduces steelmaking slag in a method for producing high phosphorous iron by reducing steelmaking slag and then dephosphorizing the high phosphorous iron to produce high phosphoric acid slag to obtain a phosphate slag fertilizer. By using the same electric furnace with arc heating for the reduction treatment furnace and the dephosphorization treatment furnace for performing the dephosphorization treatment, it is not necessary to use a converter as the dephosphorization treatment furnace. A sufficient heat source can be secured by phosphorus treatment to increase the degree of freedom of the slag composition and to reduce the viscosity of the slag.

It is a figure which shows the manufacturing method of the phosphate slag fertilizer of this invention, (A) is a reduction process, (B) is a dechromation process, (C) is a dechromation process, (D) is a dephosphorization process, (E ) Is a diagram showing a finish dephosphorization process.

  The present invention is directed to a method of reducing steelmaking slag to produce high phosphorus hot metal, and then subjecting the high phosphorus hot metal to dephosphorization to produce high phosphate slag to obtain a phosphate slag fertilizer. To do. The reduction furnace for reducing the steelmaking slag and the dephosphorization furnace for performing the dephosphorization process are the same electric furnaces equipped with arc heating. Hereinafter, it demonstrates in detail based on FIG. Unless otherwise indicated,% display about component content means the mass%.

  The electric furnace 1 used in the present invention can be either direct current or alternating current, but direct current has a larger slag agitation force, and in a direct current electric field, it has a cleaning effect of fine grain iron in the slag due to the Electro Capillary Effect. A DC electric furnace is more desirable. FIG. 1 shows a case where a DC electric furnace is used as the electric furnace 1.

  Steelmaking slag is slag collected after steelmaking refining and contains phosphoric acid and iron oxide. Usually, it has 1% or more (about 2%) phosphoric acid and about 10 to 30% iron oxide. Decarburization slag and dephosphorization slag produced by converter refining for refining blast furnace hot metal are the main steelmaking slag generation sources.

  FIG. 1A shows the implementation status of the reduction process 31. In the reduction treatment 31, a predetermined amount of steelmaking slag 13 containing phosphoric acid and iron oxide is charged into the electric furnace 1 having the arc heating 3 by the electrode 2. The steelmaking slag to be introduced may be in a molten state or a solid. FIG. 1 (A) shows a situation where a molten steelmaking slag 13 is charged from the steelmaking slag container 5. In the electric furnace 1, molten iron 11 as seed water is preferably formed in advance. A carbon material 21 as a reducing agent is introduced into the electric furnace 1 together with the steelmaking slag 13. As the carbon material 21, coal powder or coke powder is used. Arc heat is used as a heat source for reduction, and the slag 12 (steel slag 13) in the electric furnace 1 is reduced by the charged carbonaceous material 21. Phosphoric acid and iron oxide in the steelmaking slag are reduced by carbon to become phosphorus contained in the molten iron and molten iron, and mixed with the seed hot water to increase the amount of molten iron 11 in the electric furnace.

When reducing the steelmaking slag, it is preferable to add an additional iron making agent as the slag modifier 22 into the electric furnace 1. The slag modifier 22 is a material for lowering the melting point of the reduced slag, lowering the slag viscosity, and extinguishing free CaO, or a material for producing a blast furnace slag equivalent. As the SiO ₂ source of the reduced slag, fly ash, silica sand and the like are suitable, and fly ash, brick scraps and the like are used as the Al ₂ O ₃ source. The target composition of the slag after modification by the addition of the slag modifier is as follows. First, the basicity ((CaO) / (SiO ₂ ) mass ratio) is 1.5 or less, preferably 1.2 or less. This is because if the basicity is too high, the melting point increases, the fluidity decreases, and the P reduction efficiency also decreases. On the other hand, if it is too low, the energy required for SiO ₂ dissolution becomes excessive, so the lower limit of basicity is preferably 0.8. In addition, the (Al ₂ O ₃ ) component in the slag after modification is preferably 8% to 12%. This is because the required energy increases if it is too high, and the viscosity increases if it is too low.

  The steelmaking slag is reduced until the (T.Fe) component of the slag 12 is reduced to about 1% or less by introducing the carbonaceous material 21 and the arc heating 3 into the slag 12 introduced into the electric furnace 1. When the target reduction is completed, the reduced slag (reduced slag 14) is discharged from the electric furnace 1. FIG. 1 (A) shows a situation in which the reduced slag 14 is discharged from the electric furnace 1 to the reduced slag container 6. One process from when the steelmaking slag 13 is introduced into the electric furnace 1 until the reduced slag 12 is discharged is referred to as “unit reduction process”.

  When one unit reduction process is completed, the steelmaking slag 13 is newly put into the electric furnace, and the next unit reduction process is performed. A portion of the reduced slag 14 generated in the previous unit reduction treatment remains in the electric furnace in a molten state without being discharged out of the furnace, and this reduced slag 14 is charged in the next reduction of the steelmaking slag. It has a function to suppress direct reaction between slag and C in the metal and prevent slag forming.

  By performing the unit reduction process a plurality of times as described above, the molten iron 11 is sequentially increased in the electric furnace. Moreover, phosphoric acid in the steelmaking slag is reduced in the molten iron 11 to contain phosphorus, and the phosphorus concentration in the molten iron 11 increases. Then, when the amount of molten iron in the electric furnace reaches a predetermined amount of molten iron, the reduction process is terminated. In the case of a fixed electric furnace, the predetermined molten iron amount is equal to or lower than the lower end level of the slag hole, and in the case of a tilting furnace, lower than the lower end level of the slag discharge.

More specifically, the reduction process 31 will be described.
A closed electric furnace (with steady air suction) containing molten iron ([C]: 0.5% to 4.5%) as a seed bath and molten reduced slag ((T.Fe) 2% or less) Steel slag ((T.Fe) 10% or more, (P ₂ O ₅ ) 1% or more) is charged into a non-electric furnace). Steelmaking slag may be charged intermittently in a molten state, or powdered slag may be continuously charged. FIG. 1 (A) shows a situation where a molten steelmaking slag 13 is charged from the steelmaking slag container 5. While heating with arc, carbon powder (coke powder, coal powder) as reducing agent, SiO ₂ source (fly ash, silica sand, silica) and Al ₂ O ₃ source (fly ash, brick scrap, etc.) as slag component modifier ) Continuously from above.

The steelmaking slag 13 is reduced to a reduced slag 14, and after Fe and P are transferred into the molten iron 11, the reduced slag 14 is discharged out of the furnace. At this time, the slag basicity ((CaO) / (SiO ₂ )) is set to 1.5 or less in order to secure the reducing ability. The increase in iron content and the molten iron with increased P concentration may be held as they are, and the charging and reduction of the steelmaking slag may be repeated as long as the molten iron level is below the level reaching the lower end level of the slag hole or the lower end level of the discharge port. When the molten iron level reaches a predetermined level, or when the molten iron [P] reaches a predetermined level, the reduction process is terminated. The predetermined molten iron level is lower than the lower limit level of the slag hole in the case of a fixed electric furnace, and lower than the lower slag discharge level in the case of a tilting furnace.

The [P] concentration in the molten iron stored in the electric furnace by the reduction treatment is determined by the ratio of phosphoric acid and iron oxide in the steelmaking slag introduced by the reduction treatment. As the [P] concentration in the molten iron is higher, the frequency of the phosphorus concentration process in the dephosphorization process in the next step is reduced, so that the productivity is improved. The lower limit is the [P] level at which slag having (P ₂ O ₅ ) of 10% or more can be easily formed by dephosphorization. Therefore, the [P] concentration in molten iron is preferably 0.4% or more. For example, in order to make (P ₂ O ₅ ): 10% with 100 kg of dephosphorized slag, the molten iron [P] must be 0.43% or more. On the other hand, if the [P] concentration in the molten iron is too high, the amount of slag required for dephosphorization increases and the dephosphorization reaction efficiency decreases. Therefore, the upper limit is 4%.

In proceeding from the reduction process to the next process, it is preferable that the reducing slag is sufficiently discharged from the electric furnace. SiO ₂ contained in the reduced slag causes an increase in the amount of input lime necessary for dephosphorization, and Al ₂ O ₃ is not necessary for fertilizer. Therefore, reduced slag is discharged as much as possible to prevent the mixing of Al ₂ O _3. This is desirable.

  After the reduction process is completed, the molten iron stored in the electric furnace is stored in the electric furnace as it is, or after being discharged from the electric furnace, it is charged again in the same electric furnace, and the process proceeds to the next dephosphorization process. To do. The discharge from the electric furnace once is a case where the molten iron is transferred to a separate container and the dechroming process is performed in the separate container, which will be described below.

Here, the dechromation process 32 performed between the said reduction process and the dephosphorization process mentioned later is demonstrated. In the molten iron produced by reducing steelmaking slag, Cr is concentrated as well as P. The fertilizer control law stipulates that (T.Cr) in phosphate fertilizers obtained by dephosphorization treatment must be suppressed to less than 1/10 of the solubility (P ₂ O ₅ ). If only the reduction treatment and the dephosphorization treatment are performed, the Cr concentration in the produced high phosphate slag may be too high. When slag needs to be dechromed, it is necessary to discharge the molten iron as much as possible before dephosphorization in the electric furnace and dechromate it by supplying oxygen outside the electric furnace.

Therefore, in the present invention, as shown in FIG. 1 (B), in the present invention, part or all of the molten iron (molten iron before dechroming 16) generated or increased by performing the unit reduction treatment a plurality of times is temporarily removed from the electric furnace. Then, it is discharged into a separate container 9 and dechromed 32. In order to perform dechromation while suppressing dephosphorization, an oxidation treatment may be performed at a low basicity (for example, (CaO) / (SiO ₂ ) <1.2). Therefore, in the presence of slag having a mass ratio of (CaO) / (SiO ₂ ) of 1.5 or less, an oxygen source is supplied from the oxygen lance 10 or the like to the molten iron in the separate container 9 to thereby obtain the [Cr] concentration in the molten iron. Is reduced to 0.1% by mass or less. After the dechromation treatment, as shown in FIG. 1C, after the dechromation treatment is performed until the dephosphorization slag (high phosphate slag) (T.Cr) is within the specified range even after the dephosphorization treatment, The molten iron 17 is charged again into the same electric furnace 1.

  In the above dechromation treatment, the molten iron in the electric furnace is discharged in a separate container in principle, but some metal remains within a range that does not hinder energization. Oxygen is supplied to the slag discharged along with the metal discharged into a separate container to oxidize and remove Cr. The oxygen source to be supplied may be oxygen gas or a material having iron oxide (iron ore, dust, scale, etc.). When the metal [Cr] concentration is sufficiently low (0.05% or less), the dechroming process can be omitted. The chromed molten iron is charged again into the electric furnace (FIG. 1C). At this time, a flux necessary for dephosphorization may be added in advance. The purpose is the early dissolution of flux and the use of stirring power.

  The molten iron after the reduction treatment is stored in the electric furnace as it is, or once discharged from the electric furnace, the molten iron that has been subjected to the above dechromation treatment is charged again in the same electric furnace, and the next dephosphorization treatment is performed. (FIG. 1D).

In the dephosphorization process 33, as shown in FIG. 1D, the same electric furnace 1 as the electric furnace 1 used in the reduction process 31 and having an arc heating 3 is used. With respect to the high phosphorus molten iron produced by the reduction treatment, the CaO source 23 and the oxygen source 24 are put into the electric furnace 1 and arc heating 3 is performed to remove phosphorus, and the P ₂ O ₅ concentration is 10% by mass or more. The high phosphate slag 15 is manufactured. The introduction of the CaO source 23 is for increasing the basicity of the slag and promoting the dephosphorization reaction.

  The dephosphorization process 33 is an oxidation process in which phosphorus in molten iron is oxidized and transferred into slag. As the oxygen source 24 for the oxidation treatment, the present invention is characterized by using a solid oxygen source such as iron oxide instead of oxygen gas. When oxygen gas is used as the oxygen source as in the prior art, the molten iron is heated to a high temperature at the point where the blown oxygen gas comes into contact with the molten iron, and the temperature of the hot point increases. At high temperatures, the oxidation of carbon (decarburization) is prioritized over the oxidation of phosphorus in molten iron as an oxidation reaction, CO bubbles are generated and the slag is in a forming state, increasing the risk of slag overflow. Moreover, decarburization progressed rather than progress of dephosphorization. In contrast, the present invention uses a solid oxygen source such as iron oxide as the oxygen source. When iron oxide is introduced into the molten iron in the furnace, the iron oxide is reduced, and the reduction reaction is an endothermic reaction, so that the temperature of the molten iron in the reaction region decreases. As the temperature decreases, the dephosphorization reaction proceeds in preference to the decarburization reaction. Therefore, it is possible to increase the phosphoric acid concentration in the slag by dephosphorization while suppressing the decarburization of the molten iron. In addition, since the occurrence of forming is suppressed as compared with the case of using oxygen gas, it has become possible to sufficiently perform the dephosphorization process while reducing the risk of slag overflow. In addition, since the electric furnace used in the present invention has arc heating, the reaction is endothermic using solid iron oxide as the oxygen source, but the heat source is compensated for by arc heating, so there is no problem with the heat source. A dephosphorization process can be performed. As a compensation for the increase in the external heat source, it is possible to enjoy an increase in the iron source due to iron oxide reduction.

The basicity (CaO) / (SiO ₂ ) of the dephosphorization slag is set to 3 to 8. The reason is that if it is too low, the dephosphorization ability cannot be secured, and if it is too high, the melting point of the slag rises and cannot be dissolved. In order to set the basicity of the slag to 3 or more, the CaO source 23 is introduced into the electric furnace in the dephosphorization process. Further, (T.Fe) of the dephosphorized slag is in the range of 5% to 20%, preferably 5% to 15%. The reason is that if it is too low, the dephosphorization ability cannot be secured, and if it is too high, it will hinder the high concentration of (P ₂ O ₅ ).

  In order to increase the dephosphorization efficiency by the dephosphorization treatment, it is important to control the viscosity of the slag as well as the slag component. Slag has a basicity of 3 or higher and a high basicity. Since Fe is also low, the viscosity of slag increases at the same temperature.

It has been found that the addition of fluorite into the slag can reduce the viscosity of the slag. However, the present invention aims to use high phosphate slag as phosphate slag fertilizer. If slag contains fluorite, it cannot be used as a fertilizer. This is because when fluorite (CaF ₂ ) is contained, fluoroapatite is formed in which phosphoric acid is difficult to elute. Therefore, fluorite cannot be used in the present invention.

  In contrast, in the present invention, the dephosphorization treatment is performed using an electric furnace having arc heating, so that the slag temperature is increased by arc heating, and high basicity and low T.I. Even under conditions where Fe and fluorite are not used, the viscosity of the slag can be sufficiently reduced and the dephosphorization reaction can be favorably promoted. The slag temperature is ensured to be 1500 ° C. or higher, and the slag fluidity and uniformity are ensured. Adjust the temperature by arc heating. By raising the temperature by arc heating and lowering the viscosity of the slag, it becomes easy to improve the uniformity of the slag and ensure quality assurance as a fertilizer. Moreover, since the granular iron contained in the slag can be easily settled and separated, the magnetic separation process after discharge can be reduced or omitted.

As the CaO source 23 put into the electric furnace in the dephosphorization process, one or more of molten steelmaking slag, steelmaking slag powder, quick lime powder, limestone powder, and dolomite powder can be used. The steelmaking slag may be molten slag or powdered slag. Flux melting is promoted by arc heating after or during flux charging. If molten slag is used as the flux, sensible heat can be used and high basicity can be obtained at an early stage, so that the decarburization reaction can be suppressed. Cold powder slag may be used. By using steelmaking slag as a dephosphorizing agent, mineral components suitable for fertilizers such as SiO ₂ and MgO can be utilized. Also, about 20% of (FeO) can be used for dephosphorization oxidation. However, since only the steelmaking slag lacks CaO and FeO, it is necessary to add a CaO source and iron oxide separately.

  One or more of iron ore powder, dust powder, and scale powder can be used as the oxygen source 24 put into the electric furnace in the dephosphorization process. The decarburization reaction can be suppressed without using gaseous oxygen.

  In the dephosphorization process, the electric furnace does not provide the stirring force necessary for dephosphorization, and therefore it is necessary to mitigate the movement rate limiting by gas blowing. It is desirable to perform gas blowing with an insertion type nozzle or bottom blowing / side blowing gas stirring. However, since it is important to be able to stop gas blowing from the viewpoint of preventing slag foaming when charging molten slag, it is desirable to install a variable flow rate type nozzle for bottom blowing and side blowing. As the flow rate variable type nozzle, there are a small diameter nozzle, a flat nozzle, a porous nozzle, and the like, and the flow rate can be reduced when the molten slag is charged.

The target (P ₂ O ₅ ) concentration in the high phosphate slag after dephosphorization is 10% or more. This is for the purpose of producing a high-phosphate fertilizer. In the slag, (P ₂ O ₅ ) is more preferably 15% or more.

As described in Patent Document 5, the composition of slag after dephosphorization is mass%,
SiO ₂ / P ₂ O ₅ ≧ 0.4 (1)
CaO / P ₂ O ₅ ≧ 2.0 (2)
P ₂ O ₅ ≧ 10% (3)
T.A. Fe: 5% or more and 15% or less (4)
Is preferable.

As compound form of phosphoric acid which is found in ordinary general, double salts of _{5CaO · P 2 O 5 · SiO} 2 is soluble in most citric acid. According to this chemical formula, the mass ratio is CaO: P ₂ O ₅ : SiO ₂ = 1.97: 1: 0.423. When the ratio of SiO ₂ / P ₂ O ₅ satisfies the above formula (1), the phosphoric acid solubility in which slag is dissolved in citric acid is maintained at a high level. Therefore, also in the present invention, it is preferable that the composition of the slag after dephosphorization satisfies the above formula (1).

The dephosphorization slag can maintain the phosphoric acid solubility at a high level of 0.4 to 0.7 by setting the CaO / P ₂ O ₅ ratio to 2.0 or more. That is, it is preferable that the above expression (2) is satisfied.

When the slag after dephosphorization is used as a phosphate fertilizer raw material, the higher the P ₂ O ₅ concentration in the slag, the greater the value as phosphorus fertilizer. In the present invention, by satisfying the above formula (3) with P ₂ O ₅ ≧ 10%, it is possible to prevent an increase in the amount of fertilizer used when giving the necessary amount of phosphoric acid to the soil. Can be obtained. More preferably, P ₂ O ₅ ≧ 15%.

The dephosphorization reaction in the dephosphorization refining of the present invention is an oxidation reaction. Phosphorus in molten iron is oxidized using iron oxide represented by Fe concentration as an oxygen source. Therefore, the T.W. If the Fe concentration is too low, the dephosphorization ability in the dephosphorization refining is extremely lowered and the P ₂ O ₅ concentration effect is diminished. If the Fe concentration is 5% or more, the dephosphorization ability can be exhibited. On the other hand, T. in the slag. If the Fe concentration is too high, there will be an adverse effect of reducing the P ₂ O ₅ concentration in the slag. In the present invention, the slag T.I. The upper limit of Fe concentration is preferably 15%.

An attempt to increase the P ₂ O ₅ concentration in the slag under the condition of CaO / P ₂ O ₅ ≧ 2 prevents the slag dilution effect by SiO ₂ or iron oxide. It is necessary to lower Fe and increase the basicity, and such components increase the melting point and viscosity of slag. Therefore, it can be seen that increasing the temperature of the slag by arc heating of the electric furnace as in the present invention is an extremely effective means for obtaining molten slag having a uniform target composition.

  When the reduction process and the dephosphorization process in the electric furnace are finished and the molten iron and slag in the electric furnace reach the target temperature and composition, the obtained high phosphate slag is discharged from the electric furnace. FIG. 1 (D) shows a situation where high phosphate slag 15 is being transferred from the electric furnace 1 to the high phosphate slag container 7. The high phosphoric acid slag 15 can be used as it is as a phosphoric acid slag fertilizer.

  After discharging high phosphate slag from the electric furnace, molten iron remains in the electric furnace. Since the purpose of the dephosphorization treatment of the present invention is to produce high phosphate slag, the phosphorus concentration in the molten iron in the electric furnace after the dephosphorization treatment may be lowered to a point where it decreases. For this reason, the phosphorus concentration in the molten iron after the dephosphorization treatment is often higher than the normal blast furnace hot metal. If it is used as it is, it will be used as a main raw material for normal steelmaking refining, and the dephosphorization load in steelmaking refining will increase. Therefore, in the present invention, after discharging the high phosphate slag 15 from the electric furnace (FIG. 1 (D)), the molten iron is left in the furnace, and as shown in FIG. It is preferable that quick lime or limestone and iron oxide be added to the steel to carry out a treatment (final dephosphorization treatment 34) for reducing the [P] concentration in the molten iron to 0.15% by mass or less, preferably 0.12% by mass or less. In the final dephosphorization process 34, quick lime powder, limestone powder and iron oxide powder are added, and gas stirring is performed, and arc heating is performed as necessary. Since the purpose of the final dephosphorization treatment is to reduce the molten iron [P], dephosphorization is performed by charging quick lime or limestone (CaO source 23) and iron oxide (oxygen source 24) instead of steelmaking slag. Achieve your goal with as little slag as possible. After the finish dephosphorization treatment, the molten iron is discharged from the electric furnace, and can be used as a steelmaking raw material together with a normal blast furnace hot metal. In FIG. 1 (E), dephosphorized molten iron 18 is transferred to the ladle 8. In the electric furnace, the molten iron required as seed water for the next reduction treatment is left. Depending on the [P] level, the discharged dephosphorized molten iron 18 can be used as molten iron, charged in the converter as molten steel, solidified, solidified and charged into the converter as iron scrap, etc. .

  After the final dephosphorization treatment, slag and some molten iron as the next seed water remain in the furnace. In the present invention, the next reduction treatment is started while leaving the slag and seed hot water remaining. Thereby, the slag refined by the finish dephosphorization treatment can be directly reduced and recovered by the next reduction treatment.

Here, the [C] concentration in the molten iron in the reduction treatment and the dephosphorization treatment of the present invention will be described.
At the time of slag reduction in the reduction treatment, charging the steelmaking slag into the reduction treatment furnace in a molten state is effective from the viewpoint of reducing required energy. At that time, in order to prevent bumping and achieve stable operation, the molten iron [C] formed in the electric furnace should be low. In the present invention, since arc heating can be used as external energy, even when the molten iron [C] after the reduction treatment and before the dephosphorization falls, there is no shortage of heat during the dephosphorization treatment. It is possible to reduce the medium [C] concentration.

In the dephosphorization treatment, in the present invention, the concentration of the molten iron [C] after the dephosphorization treatment can be increased by suppressing the decarburization reaction and promoting the dephosphorylation reaction, and the heat source in the next step can be maintained. . Moreover, slag forming during dephosphorization can be suppressed by suppressing the decarburization reaction. As methods for suppressing the decarburization reaction, there are the following methods, and external heating such as arc heating is effective for any of them.
(1) Early increase of slag basicity (decrease in P ₂ O ₅ activity) by arc melting of CaO powder or use of molten decarburized slag and suppression of decarburization (2) Iron oxide instead of oxygen as oxygen source Application and preferential decarburization due to temperature reduction in dephosphorization reaction zone

  Using a DC electric furnace having arc heating, phosphate slag fertilizer was produced according to the present invention under the conditions shown in Table 1. Table 1 shows typical components of molten iron and slag.

  In the electric furnace before the start of the reduction treatment, 70 tons of molten iron as seed water and 26.5 tons of molten slag are accommodated. As the reduction process, a process of repeating the unit reduction process six times was performed. In each unit reduction treatment, 30 tons of steelmaking slag and 3.6 tons of charcoal are put into an electric furnace. Table 1 shows the amount of molten iron and slag in the furnace and the amount of discharged slag after the first unit reduction treatment and after the sixth unit reduction treatment. At the end of the reduction treatment, 121.3 tons of molten iron was contained in the furnace. After the sixth unit reduction treatment and slag discharge, 120 tons of molten iron was discharged into a separate container for the dechromation treatment.

The molten iron after the dechroming treatment was again charged into the electric furnace, and dephosphorizing treatment was performed under the conditions shown in Table 1. The iron oxide added in the dephosphorization process was reduced, and the molten iron increased to 124 tons. The (P ₂ O ₅ ) concentration in the furnace slag (22 tons) after the dephosphorization process reached 17.0%, and a high phosphate slag could be formed.

  After discharging 20 tons of high phosphoric acid slag from the electric furnace, a finish dephosphorization treatment was further performed under the conditions shown in Table 1. Since the [P] concentration in the molten iron decreased to 0.08%, 56 tons of this molten iron was discharged from the electric furnace and could be used together with the blast furnace hot metal as the main raw material for ordinary steelmaking. Since 70 tons of molten iron and 6.2 tons of slag remained in the electric furnace, it was possible to start the next reduction treatment using the molten iron as a seed hot water.

As steelmaking slag containing phosphoric acid and iron oxide, those shown in Table 2 as representative components were prepared. This steelmaking slag and charcoal are put into an electric furnace, arc heating is performed, steelmaking slag is reduced by the supplied charcoal, and the reduced slag (reduced slag) is discharged from the electric furnace (unit reduction treatment) ) Was performed a plurality of times to carry out the reduction treatment, and high phosphorous molten iron was produced in the electric furnace, and reduced slag was formed thereon. Reduced slag was discharged from the electric furnace. Then, the dephosphorization process shown in the following comparative examples and inventive examples 1 to 4 was performed using 100 tons of high-phosphorus molten iron (components and temperatures shown in Table 3) generated in the electric furnace. The results are shown in Table 3. In the “Steelmaking slag” column of Table 3, “Cold” means solid steelmaking slag, and “Hot” means molten steelmaking slag. In the column of additive / oxygen gas in Table 3, the added basic unit (kg / t or Nm ³ / t) per ton of molten iron is described.

[Comparative example]
In the converter, after charging the high phosphorus hot metal, 7.5t of quick lime, 5.0t of iron ore, 1.8t of silica sand, 5.0t of light calcined dolomite, and 300Nm ³ / h nitrogen bottom blowing stirring Then, oxygen was blown over to remove 100 t of high-phosphorus molten iron. The oxygen blowing amount was 12000 Nm ³ / h × 20 min / 60 = 4000 Nm ³ . The hot metal conditions before dephosphorization were [C]: 4.5%, [P]: 2.1%, and hot metal temperature 1350 ° C.
After feeding the acid and flux, the iron bath conditions were [C]: 0.2%, [P]: 0.14%, temperature: 1620 ° C., and the slag conditions were (T.Fe): 18.0% , (P ₂ O ₅ ): 18.8%, (CaO) / (SiO ₂ ): 4.2, and slag amount: 22.5 t.

The temperature of the slag metal was raised with the combustion heat of C, P, and Fe. After dephosphorization, it was solidified and charged into the converter as iron scrap. Since melting of the flux took time and decarburization reaction was preceded, intense forming occurred.
The produced slag had a composition suitable for fertilizer, but it was poor in uniformity and contained a large amount of granular iron. Moreover, even though [C] in molten iron dropped to 0.2%, [P] remained at 0.2%, so final dephosphorization could not be performed sufficiently. Used in the furnace.

[Invention Example 1]
[C]: 3.5%, [P]: 2.0%, [Cr]: 0.03% obtained by reduction using a direct current reduction electric furnace used for reduction, 100 t of molten iron at a temperature of 1350 ° C. Was charged into an electric furnace as high phosphorus molten iron.
When dephosphorizing high phosphorus molten iron, converter decarburized slag pulverized to 3 mm or less as a CaO source: 14.8 t, quicklime powder: 4.0 t, iron ore powder: 11.8 t as an oxygen source in about 60 minutes It was continuously put into the electric furnace. At the same time, arc heating was performed at 20 MW for 60 minutes to completely dissolve the flux. Thereafter, the energization was stopped, an immersion lance was inserted, and stirring was performed for 15 minutes. The slag was reheated at 25 MW for an additional 15 minutes to increase fluidity.

As a result, the conditions of the iron bath after the treatment were [C]: 2.5%, [P]: 0.12%, the temperature: 1615 ° C., and the slag conditions were (T.Fe): 12.1%, (P ₂ O ₅ ): 18.9%, (CaO) / (SiO ₂ ): 4.9, and slag amount: 23.0 t, and a high phosphate slag could be produced. At this time, the power consumption was 26.1 MWh.
Since oxygen gas was not used as the oxygen source and iron ore was used as the oxygen supply source, the temperature of the reaction site could be kept low, so that the dephosphorization reaction was promoted and the slag forming was gentle. Moreover, since the decarburization reaction was suppressed, [C] was maintained at 2.5% even after the treatment was completed.
The fluidity of the slag was good and uniform properties with almost no granular iron, and high phosphate slag with a high fertilizer effect could be obtained.
Since the metal [P] after dephosphorization is usually at a hot metal level, it was charged in a torpedo car as it was, mixed with normal hot metal and then sent to the converter process. [C] was lower than the normal hot metal, but the temperature was high, so there was no shortage of heat source.

[Invention Example 2]
In the same manner as in Example 1 of the present invention, dephosphorization treatment was performed on the high-phosphorus molten iron whose concentration was advanced to 3.2% [P].
Since the amount of dephosphorization increased, the calorific value increased, but the slag amount increased to 36.0 t, so the power consumption increased from 26.1 MWh to 32.8 MWh.

[Invention Example 3]
In the same manner as in Example 1 of the present invention, the dephosphorization treatment was performed on the molten iron whose [C] decreased to 2.5% in the reduction step. Since the amount of decarburization decreased, the amount of heat generated by oxidation decreased, and the power consumption amounted to 23.3 MWh.

[Invention Example 4]
In the same manner as in Example 1 of the present invention, dephosphorization of high phosphorus molten iron was performed. The steelmaking slag used as a flux was intermittently charged into an electric furnace while being in a molten state. After completion of charging, quick lime powder and iron ore powder were continuously charged, and arc heating was performed while simultaneously controlling forming at 20 to 30 MW. Although the components and temperature after the treatment were almost the same as those of Example 1 of the present invention, the power consumption was reduced to 20.5 MWh because the sensible heat of the steelmaking slag at 1300 ° C. could be used.

DESCRIPTION OF SYMBOLS 1 Electric furnace 2 Electrode 3 Arc heating 4 Lance 5 Steelmaking slag container 6 Reduction slag container 7 High phosphate slag container 8 Ladle 9 Separate container 10 Oxygen lance 11 Molten iron 12 Slag 13 Steelmaking slag 14 Reduction slag 15 High phosphate slag 16 Desorption Molten iron before chromium 17 Molten iron after dechromation 18 Dephosphorized molten iron 21 Carbon material 22 Slag modifier 23 CaO source 24 Oxygen source 31 Reduction treatment 32 Dechromation treatment 33 Dephosphorization treatment 34 Additional dephosphorization treatment

Claims (5)

Steelmaking slag containing phosphoric acid and iron oxide and charcoal are put into an electric furnace, arc heating is performed, steelmaking slag is reduced by the supplied charcoal, and the reduced slag (reduced slag) is electric furnace The process of discharging from the unit is called “unit reduction process”
The molten iron generated or increased by performing the unit reduction treatment once or a plurality of times is stored in the electric furnace as it is, or once discharged from the electric furnace and then charged again in the same electric furnace,
Phosphorus characterized in that a high-phosphate slag having a P ₂ O ₅ concentration of 10% by mass or more is produced by introducing a CaO source and an oxygen source into an electric furnace and performing arc heating to dephosphorize the molten iron. Method for producing acid slag fertilizer. The CaO source to be charged into the electric furnace in the dephosphorization treatment is one or more of molten steelmaking slag, steelmaking slag powder, quick lime powder, limestone powder, dolomite powder,
The method for producing phosphate slag fertilizer according to claim 1, wherein the oxygen source is one or more of iron ore powder, dust powder, and scale powder.   In the dephosphorization process, gas injection by lance insertion, or a variable flow rate gas injection tuyere or nozzle at the bottom or wall of an electric furnace to introduce gas into the iron bath and to stir the iron bath The manufacturing method of the phosphate slag fertilizer of Claim 1 or Claim 2 characterized by the above-mentioned. A part or all of the molten iron generated or increased by performing the unit reduction treatment once or a plurality of times is once discharged from the electric furnace to another container,
In the presence of slag having a mass ratio of (CaO) / (SiO ₂ ) of 1.5 or less, an oxygen source is introduced into the molten iron in the separate container to reduce the [Cr] concentration in the molten iron to 0.1 mass% or less. The method for producing phosphate slag fertilizer according to any one of claims 1 to 3, wherein the molten iron is reduced and charged in the same electric furnace again.   The high phosphoric acid slag is discharged from the electric furnace, and quick lime or limestone and iron oxide are added into the electric furnace to reduce the [P] concentration in the molten iron to 0.15 mass% or less (hereinafter referred to as “finish dephosphorization”). 2. After the treatment is performed, the molten iron is discharged and used as a raw material for steelmaking, and the next reduction treatment is started while leaving the slag and molten iron remaining in the furnace. The manufacturing method of the phosphate slag fertilizer of any one of Claims 1-4.

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