JP2014001456A - Recovery method for iron and phosphorus from steel slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recovery method for iron and phosphorus from steel slag that can effectively and individually utilize the phosphorus and the iron recovered as resources while recovering the phosphorus and the iron from the steel slag at low costs when the steel slag containing the phosphorus such as dephosphorized slag is recycled.SOLUTION: A recovery method for iron and phosphorus from steel slag includes: a first step of causing phosphorus-containing steel slag to be subjected to a reduction treatment by using reducing agents such as carbon, Si and Al and reducing and recovering iron oxide and phosphorus oxide in the slag as phosphorus-containing molten iron; a second step of using the steel slag from which the iron oxide and the phosphorus oxide are removed as a CaO source in a sintering step and recycling sintered ore manufactured in a blast furnace; a third step of causing the phosphorus-containing molten iron recovered by the reduction treatment to be subjected to a dephosphorizing treatment until the phosphorus concentration in the phosphorus-containing molten iron becomes 0.1 mass% or less and condensing phosphorus in CaO-based flux; and a fourth step of mixing the phosphorus-containing molten iron having the phosphorus concentration of 0.1 mass% or less as an iron source with blast furnace molten iron.

Description

  The present invention relates to a method for recovering iron and phosphorus contained in steelmaking slag from steelmaking slag containing phosphorus such as dephosphorization slag produced by a preliminary dephosphorization treatment of hot metal.

  Due to the iron ore component, the hot metal melted in the blast furnace contains phosphorus (P). Since phosphorus is a harmful component for steel materials, dephosphorization has been conventionally performed in the steel making process in order to improve the material properties of steel products. In this dephosphorization process, in general, phosphorus in molten iron or molten steel is oxidized by oxygen gas or iron oxide, and then the oxidized phosphorus is fixed in slag mainly composed of CaO. Has been removed. When phosphorus in hot metal or molten steel is oxidized with oxygen gas, iron is also oxidized, and even when iron oxide is not added, iron is also contained in the form of iron oxide in the slag. Steelmaking slag containing phosphorus, which is generated by hot metal preliminary dephosphorization and decarburization refining in a converter, has been conventionally discharged out of the steelmaking process as civil engineering materials. The phosphorus and iron are not recovered. The preliminary dephosphorization treatment is a treatment for removing phosphorus in the hot metal in advance before decarburizing and refining the hot metal in a converter.

  In recent years, from the viewpoint of environmental measures and resource saving, reducing the amount of steelmaking slag generated, including the recycling of steelmaking slag. For example, slag generated in converter decarburization refining of hot metal that has been subjected to preliminary dephosphorization treatment (slag generated in converter decarburization refining is referred to as “converter slag”) is used as an iron source and a CaO source for a slagging agent. Recycling to a blast furnace through a sintering process and recycling as a CaO source in a hot metal pretreatment process are performed.

  Pre-dephosphorized hot metal (also referred to as “dephosphorized hot metal”), particularly converter slag generated in converter decarburization of pre-dephosphorized hot metal pre-dephosphorized to the product phosphorus concentration level, contains almost no phosphorus. It is not necessary to worry about the increase (pickup) of phosphorus concentration in hot metal by recycling to blast furnace without containing, but slag generated during preliminary dephosphorization treatment or hot metal that has not been pre-dephosphorized ("normal hot metal") Also, the phosphorus concentration after dephosphorization is not reduced to the phosphorus concentration level of the product even though it has been preliminarily dephosphorized. In the slag contained, phosphorus recycled to the blast furnace as an oxide is reduced in the blast furnace to increase the phosphorus content of the hot metal, resulting in a vicious cycle in which the load of dephosphorization from the hot metal increases. Therefore, various proposals have been made for recycling phosphorus-containing steelmaking slag, particularly for recycling to processes involving refining, in order to prevent phosphorus pickup. Of course, also in the case of recycling to an oxidation step such as preliminary dephosphorization, the function as a dephosphorizing agent is impaired and the amount recycled is limited.

  For example, in Patent Document 1, when melting molten stainless steel by a combination of a smelting reduction smelting process of chromium ore and a converter decarburization refining process of chromium-containing hot metal melted by the smelting reduction smelting process, The carbon material is added to the dephosphorization slag generated by the dephosphorization treatment of the chromium-containing hot metal and heated, and the dephosphorization slag is vaporized and dephosphorized, and the dephosphorized slag after the vaporization and dephosphorization treatment is subjected to the smelting reduction smelting A technique for recycling to a process is disclosed.

In Patent Document 2, molten blast furnace slag and molten converter slag are mixed, and at least one of carbon, silicon, and magnesium is added to the mixed slag, and oxygen gas is blown into the mixed slag. in, and phosphorus vapor by reducing phosphorus oxide in the mixed slag, and sulfur in the mixed slag (S) and SO _2, these were volatilized phosphorus and sulfur less slag and without, the slag blast furnace or A technique for recycling to a converter is disclosed.

  Furthermore, Patent Document 3 discloses that a dephosphorization slag produced by dephosphorization of hot metal or molten steel using a fouling agent mainly composed of an alkali metal carbonate is treated with water and carbon dioxide gas to produce an alkali metal. A technique is disclosed in which an extract containing a phosphate is obtained, a calcium compound is added to the extract, and phosphorus is precipitated as calcium phosphate to be separated and recovered.

JP 2004-143492 A JP-A-55-97408 JP-A-56-22613

  However, the above prior art has the following problems.

  That is, in Patent Document 1, the dephosphorization slag can be recycled after the phosphorus is removed by vaporization and dephosphorization, but the vaporized and dephosphorized phosphorus is not recovered and is effective from the viewpoint of securing phosphorus resources. It is not a recycling method.

  In Patent Document 2, blast furnace slag, which is the same amount as converter slag, is mixed with converter slag, which is phosphorus-containing slag, but in recent years, blast furnace slag is not a waste but a utility value for civil engineering and building materials. It is economically disadvantageous to use such blast furnace slag for diluting converter slag.

  Further, Patent Document 3 is a wet process, and in the case of a wet process, not only chemicals necessary for the process are expensive, but also a large-scale processing facility is required, and both the equipment cost and the operation cost are expensive.

  The present invention has been made in view of the above circumstances, and its purpose is to recover phosphorus and iron at low cost from steelmaking slag when recycling steelmaking slag containing phosphorus such as dephosphorization slag and converter slag. In addition, it is an object of the present invention to provide a method for recovering iron and phosphorus from steelmaking slag that can effectively utilize the recovered phosphorus and iron as resources.

  The method for recovering iron and phosphorus from steelmaking slag according to the first invention for solving the above-mentioned problem is a method for recovering steelmaking slag containing phosphorus generated in a steelmaking refining process, by using one or more of carbon, silicon, and aluminum. A first step of reducing and recovering iron oxide and phosphorous oxide in the steelmaking slag from the steelmaking slag as phosphorus-containing molten iron in a molten state; A second step of recycling the steelmaking slag from which the phosphorus oxide has been removed as a CaO source in the ironmaking step or the steelmaking step, and the phosphorus-containing molten iron recovered by the reduction treatment using a CaO-based flux not containing fluorine. The third step of dephosphorizing until the phosphorus concentration in the phosphorus-containing molten iron becomes 0.1% by mass or less, and concentrating phosphorus in the CaO-based flux, and the dephosphorization treatment was performed. Concentration of 0.1 wt% or less of phosphorus-containing molten iron, and is characterized in that it has a fourth step of mixing the tapping blast furnace hot metal from a blast furnace as an iron source.

  In the method for recovering iron and phosphorus from steelmaking slag according to the second invention, in the first invention, the slag generated in the decarburization refining of the hot metal in the converter is subjected to the reduction treatment in the first step. It is characterized by.

  The method for recovering iron and phosphorus from steelmaking slag according to the third invention is the method for recovering iron and phosphorus from the steelmaking slag according to the first invention, the slag generated in the decarburization refining of the hot metal in the converter, and the slag generated in the preliminary dephosphorization treatment of the hot metal. The mixture is subjected to the reduction treatment in the first step.

  In the method for recovering iron and phosphorus from steelmaking slag according to the fourth invention, in any one of the first to third inventions, the phosphorus-containing molten iron is a hot metal containing 3% by mass or more of carbon. It is a feature.

  The method for recovering iron and phosphorus from steelmaking slag according to the fifth invention is characterized in that, in any of the first to fourth inventions, the reduction treatment in the first step is performed in the presence of blast furnace hot metal. It is what.

  The method for recovering iron and phosphorus from steelmaking slag according to the sixth aspect of the present invention is the method for recovering iron and phosphorus from any one of the first to fifth aspects, wherein the steelmaking slag recycling destination in the second step is an iron ore sintering step or It is a hot metal production process in a blast furnace.

  The method for recovering iron and phosphorus from steelmaking slag according to the seventh invention is the method of recovering iron and phosphorus from any one of the first to fifth inventions, wherein the steelmaking slag recycling destination in the second step is a dephosphorization step of hot metal or It is a hot metal decarburization refining process in a furnace.

  According to an eighth aspect of the present invention, there is provided a method for recovering iron and phosphorus from a steelmaking slag according to any one of the first to seventh aspects, wherein the CaO-based flux for enriching phosphorus used in the third step is a phosphorus resource. It is characterized by being used as.

  According to the present invention, it contains phosphorus such as dephosphorization slag generated by the preliminary dephosphorization treatment of hot metal, and converter slag generated by converter decarburization refining using dephosphorization hot metal that is not sufficiently molten or dephosphorized. In recycling steelmaking slag, first, iron oxide and phosphorous oxide in steelmaking slag are reduced and recovered as phosphorus-containing molten iron, and the steelmaking slag from which iron oxide and phosphorous oxide have been removed is the steelmaking process or the steelmaking process. The phosphorus-containing molten iron is recycled to a phosphorus concentration of 0.1% by mass or less and mixed with the blast furnace hot metal, while the phosphorus in the phosphorus-containing molten iron is CaO by the dephosphorization treatment. In the system flux, it is concentrated to a level sufficient to be recovered as phosphorus resources, so that the concentration of phosphorus in the hot metal is increased in the steelmaking slag making process or recycling for use in the steelmaking process, or Without causing problems such as impairing the function as phosphorus agent, it is achieved to effectively utilize the iron contained in the steelmaking slag and phosphorus as a resource, respectively.

It is a figure which shows the schematic of the dephosphorization processing equipment used by this invention. It is a figure which shows the behavior of phosphorus during the dephosphorization process of high phosphorus hot metal.

  Hereinafter, the present invention will be described in detail.

  The present inventors have found that the dephosphorization slag generated during the preliminary dephosphorization of hot metal, and the phosphorus concentration after dephosphorization is higher than the phosphorus concentration level of the product even if the hot metal or the preliminary dephosphorization is performed. When recycling steelmaking slag containing phosphorus such as converter slag generated during converter decarburization and refining using phosphorus hot metal in the steelmaking process or steelmaking process as a CaO source for dephosphorizing agent or ironmaking agent, First, it was studied to eliminate the influence of phosphorus contained in the steelmaking slag on the hot metal discharged from the blast furnace.

  The converter slag generated during decarburization and refining of hot metal that has been pre-dephosphorized to the phosphorus concentration level of the product in advance has not been picked up by the phosphorus concentration in the hot metal, but has been subjected to the iron ore sintering process and the blast furnace. Recycled as a slagging agent. Therefore, if phosphorus is removed from the phosphorus-containing steelmaking slag, it can be recycled into a blast furnace. Therefore, removal of phosphorus from the steel slag containing phosphorus was examined.

In phosphorus-containing steelmaking slag, phosphorus is contained as an oxide of P ₂ O ₅ , and generally steelmaking slag is mainly composed of CaO and SiO ₂ , and phosphorus is calcium (Ca) and silicon ( Since the affinity for oxygen is weak compared to Si), P ₂ O ₅ in phosphorus-containing steelmaking slag can be easily reduced if phosphorus-containing steelmaking slag is reduced with carbon, silicon, aluminum, or the like. I understood. In this case, the phosphorus-containing steelmaking slag, iron in the form of FeO and Fe ₂ O ₃ (hereinafter, collectively referred to as "Fe _x O") are contained in the oxides, these iron oxide oxygen It has been found that when phosphorus-containing steelmaking slag is reduced with carbon, silicon, aluminum, etc., Fe _x O in the steelmaking slag is reduced at the same time.

  It was also found that phosphorus has high solubility in iron, and phosphorus produced by reduction dissolves rapidly in iron produced by reduction. Here, the present invention aims to remove phosphorus from the phosphorus-containing steelmaking slag and to reform it into a steelmaking slag having a low phosphorus content. In order to quickly separate the phosphorus produced by the reduction from the steelmaking slag, It has been found that it is desirable to reduce at a high temperature so that the iron produced by the reduction is in a molten state. That is, if the iron produced | generated by reduction | restoration is a molten state, the originally melted iron will be easy to isolate | separate from slag, and isolation | separation from the steelmaking slag of the iron produced | generated by reduction | restoration will be accelerated | stimulated. In addition, it was found that the phosphorus produced was dissolved in the molten iron, thereby speeding up the separation of phosphorus from the steelmaking slag. It has been found that when steelmaking slag is in a molten state, separation from iron containing phosphorus is further promoted.

  In this case, the lower the melting point of the molten iron produced, the more the separation of the molten iron and slag is promoted. Therefore, it is preferable to dissolve the carbon in the produced molten iron and produce molten iron as the molten iron. I understand. Specifically, when the carbon concentration is 3% by mass or more, the liquidus temperature of the hot metal becomes 1300 ° C. or less. Therefore, it was found that it is preferable to secure the carbon concentration of the hot metal at 3% by mass or more. In order to dissolve carbon in the produced molten iron, carbon is used as a reducing agent, or when silicon or aluminum is used as a reducing agent, the molten iron produced by coexisting carbon with steelmaking slag. Is carburized to become a hot metal containing a high concentration of phosphorus (referred to as “high phosphorus hot metal” to distinguish this hot metal from blast furnace hot metal).

  Moreover, by separately charging blast furnace hot metal in advance and performing reduction treatment in a state where the blast furnace hot metal coexists with phosphorus-containing steelmaking slag, all of the above conditions are satisfied and the separation of phosphorus from the steelmaking slag is promoted. I also understood that. That is, it has been found that it is preferable to perform a reduction treatment of phosphorus-containing steelmaking slag by separately charging a blast furnace hot metal in advance if the conditions allow hot metal to be procured.

  Since the mass ratio (P / Fe) of phosphorus and iron in the phosphorus-containing steelmaking slag is 0.005 to 0.075, phosphorus is reduced to 0.5 to 7.7 in the molten iron (high phosphorus hot metal) after reduction. About 5% by mass is contained. On the other hand, the phosphorus content of the blast furnace molten iron discharged from the blast furnace is currently about 0.1% by mass. Therefore, when high phosphorus hot metal having a phosphorus concentration of 0.5 to 7.5% by mass cannot be dephosphorized to the level of blast furnace hot metal having a phosphorus concentration of about 0.1% by mass, the operation of the high phosphorus hot metal is limited. In some cases, it may not be used as an iron source.

  Therefore, the phosphorus concentration is 4.0 mass% (level 1), 2.0 mass% (level 2), 1.1 mass using the dephosphorization equipment currently used for the preliminary dephosphorization treatment of the blast furnace hot metal. Blast furnace hot metal adjusted to 4 levels of% (level 3) and 0.5 mass% (level 4) was used as an alternative to high phosphorus hot metal, and a dephosphorization test was conducted. The phosphorus concentration of the blast furnace hot metal was adjusted using an iron-phosphorus alloy.

  In FIG. 1, the schematic of the used dephosphorization processing equipment is shown. In FIG. 1, a hot metal ladle 4 containing a high phosphorus hot metal 2 having a adjusted phosphorus concentration is loaded on a carriage 5 and carried into a dephosphorization processing facility 1. The dephosphorization processing equipment 1 is provided with an upper blowing lance 6 and an injection lance 7 that can move up and down in the hot metal ladle 4. From the upper blowing lance 6, an iron oxide such as oxygen gas or iron ore is provided. Is sprayed onto the high phosphorus hot metal 2, and CaO-based flux or iron oxide is blown into the high phosphorus hot metal 2 from the injection lance 7. The dephosphorization processing equipment 1 is further provided with raw material supply equipment such as a hopper and a chute for adding CaO-based flux and iron oxide to the inside of the hot metal ladle 4 but is omitted in FIG. Yes.

Using this dephosphorization processing equipment 1, oxygen gas is blown from the top blowing lance 6, and at the same time, a powdered CaO-based flux is blown from the injection lance 7 using nitrogen gas as a carrier gas to remove phosphorus Processing was carried out. The blown CaO-based flux melts to form dephosphorization slag 3. In this case, phosphorus in the high phosphorus hot metal is oxidized by oxygen gas to become P ₂ O ₅ and is taken into the hatched CaO-based flux, and dephosphorization of the high phosphorus hot metal 2 proceeds. Table 1 shows the experimental conditions. In addition, quick lime is used as a CaO type | system | group flux, and does not contain fluorine sources, such as a fluorite. In addition, when a predetermined amount of CaO is added to the hot metal, it may be used together with the injection lance 7 and sprayed onto the hot metal bath surface together with oxygen gas from the top blowing lance 6.

  FIG. 2 shows the behavior of phosphorus in the high phosphorus hot metal in the dephosphorization treatment performed in the experiment. As shown in FIG. 2, it was found that the dephosphorization reaction rate was higher as the phosphorus concentration in the hot metal before the start of the dephosphorization treatment was higher. Further, even with a dephosphorization treatment method generally performed on blast furnace hot metal, dephosphorization treatment up to about 0.1% by mass of phosphorus equivalent to blast furnace hot metal is performed on high phosphorus hot metal 2. I found it possible. And, it was confirmed that the high phosphorus hot metal 2 after the dephosphorization treatment can be used by mixing with the blast furnace hot metal as an iron source without any difference from the blast furnace hot metal.

Table 2 shows the composition of the dephosphorization slag produced by this dephosphorization treatment. In order to effectively use this dephosphorization slag as a phosphorus resource, it is preferable to set it to a level equivalent to 3CaO · P ₂ O ₅ (mass ratio of CaO and P ₂ O ₅ = 54: 46) which is the composition of phosphate ore. Therefore, the dephosphorization slag was aimed to contain at least 20% by weight of P ₂ O ₅ .

As shown in Table 2, the dephosphorization slag produced contains 20% by mass of P ₂ O ₅ even if the phosphorus concentration in the hot metal before the dephosphorization treatment is level 4 of 0.5% by mass. further, P ₂ O ₅ concentration levels 1 and level 2, dephosphorization slag is higher than CaO concentration, it was found that further P ₂ O ₅ than the composition of 3CaO · P ₂ O ₅ is concentrated. That is, it was found that the dephosphorized slag produced can be sufficiently utilized as a phosphorus resource.

  In addition, it is known that the CaO-based flux used for the preliminary dephosphorization treatment of the blast furnace hot metal promotes the dephosphorization reaction by promoting the hatching of CaO by adding about 5% by mass of a fluorine source such as fluorite. However, when the generated dephosphorized slag is used as, for example, a phosphorus fertilizer, fluorine is eluted from the phosphorous fertilizer (dephosphorized slag), and the fluorine elution value becomes a problem with respect to the soil environmental standards. In the present invention, no fluorine source is used.

  The present invention has been made based on the above test results, and the method for recovering iron and phosphorus from the steelmaking slag according to the present invention includes a steelmaking slag containing phosphorus generated in the steelmaking refining process, carbon, silicon, A reduction treatment using a reducing agent containing one or more of aluminum, and reducing and recovering iron oxide and phosphorous oxide in the steelmaking slag as molten phosphorus-containing molten iron from the steelmaking slag A step, a second step of recycling the steelmaking slag from which iron oxide and phosphorous oxide have been removed as a CaO source in the ironmaking step or the steelmaking step, and the phosphorus-containing molten iron recovered by the reduction treatment contains fluorine. A third step of dephosphorizing until the phosphorus concentration in the phosphorus-containing molten iron becomes 0.1% by mass or less using a CaO-based flux not concentrated, and concentrating phosphorus in the CaO-based flux; And a fourth step of mixing the phosphorus-containing molten iron having a phosphorus concentration of 0.1% by mass or less, which has been subjected to the dephosphorization treatment, with blast furnace hot metal discharged from a blast furnace as an iron source. And

  According to the present invention configured as described above, phosphorus such as dephosphorization slag generated by the preliminary dephosphorization treatment of hot metal, converter slag generated by converter decarburization refining using normal hot metal or dephosphorization hot metal with insufficient dephosphorization, etc. In recycling steelmaking slag containing iron, first, iron oxide and phosphorous oxide in steelmaking slag are reduced and recovered as phosphorus-containing molten iron, and the steelmaking slag from which iron oxide and phosphorous oxide have been removed is subjected to a steelmaking process or Recycled as a CaO source in the steelmaking process, the phosphorus-containing molten iron is dephosphorized to a phosphorus concentration of 0.1% by mass or less and mixed with the blast furnace hot metal, while the phosphorus in the phosphorus-containing molten iron is dephosphorized. As a result, the iron and phosphorus contained in the steelmaking slag can be reduced without causing adverse effects such as increasing the phosphorus concentration in the hot metal. Re it is achieved to effectively utilize the resources.

  Note that the converter slag generated during the decarburization refining of the hot metal, which has been preliminarily dephosphorized to the phosphorus concentration level of the product, also contains phosphorus, not zero. Therefore, it is possible to apply the present invention to this converter slag, but the slag has a low phosphorus content, and even if recycled to a blast furnace as it is, the influence of phosphorus can be ignored. By applying the invention, the cost is increased. Therefore, the steel-making slag containing phosphorus, which is the subject of the present invention, is higher than the concentration that increases the phosphorus concentration of hot metal or molten steel when the steel-making slag is recycled to a blast furnace or the like, and causes an increase in cost for normal operations. This steelmaking slag contains phosphorus.

  As a method of recycling steelmaking slag from which iron oxide and phosphorous oxide have been removed by reduction treatment, as described above, it is used as a CaO source (slagging agent) in the iron ore sintering step, and then in a blast furnace. In addition to the method used as the charging raw material in the hot metal production process, as a method directly used as a iron making agent in the hot metal production process in the blast furnace, or as a CaO-based flux as a dephosphorizing agent in the preliminary dephosphorization treatment of the blast furnace hot metal Preferred examples include the method used, the method used as a slagging agent in the decarburizing and refining process of hot metal in a converter, and the method used as a CaO-based desulfurizing agent in the desulfurization treatment of blast furnace hot metal. It is done. Even if it is a process other than this, as long as it is the iron making process and steelmaking process in an ironworks, if it is a process using quicklime, it can be used as a substitute for quicklime.

  Furthermore, an example of a steel-making slag containing phosphorus that is suitable for practicing the present invention is as follows. Converter slag alone generated by converter decarburization and refining using dephosphorized hot metal that is not sufficiently molten or dephosphorized. A mixture of the converter slag and the dephosphorization slag generated by the preliminary dephosphorization treatment of the hot metal is preferable.

This is because the converter slag has a high basicity (mass% CaO / mass% SiO ₂ ) (usually about 3 to 5) and is advantageous as a CaO source in the iron ore sintering process in the second step. However, since converter slag has a high basicity and is inferior in hatchability during the sintering process, dephosphorization slag may be mixed with the converter slag in order to increase hatchability. The dephosphorization slag has a basicity of about 1.5 to 2.5, and the hatchability is improved by the contained SiO ₂ . In other words, when a mixture of converter slag and dephosphorization slag is used, the sintering process can be performed smoothly without using a fluorine source, and phosphorus-containing molten iron phosphorus can be used. Since the concentration is increased, the phosphorus concentration of the CaO-based flux recovered in the third step after the dephosphorization treatment is increased, and the utilization as a phosphorus resource is promoted. However, the use of dephosphorized slag alone is not preferable because the basicity is low and the CaO source is insufficient in the sintering process.

In addition, when a mixture of converter slag and dephosphorization slag is used as the steelmaking slag to be subjected to the reduction process in the first step, hatching of the steelmaking slag reduced by SiO ₂ contained in the dephosphorization slag. In addition, the effect of promoting the separation of the phosphorus-containing molten iron obtained by reduction and the steelmaking slag during the reduction treatment is also exhibited.

  The total amount of converter slag generated may be used for the reduction treatment in the first step of the present invention, but the use of converter slag in the hot metal preliminary dephosphorization treatment is also effective from the viewpoint of resource saving. Therefore, a part of the generated converter slag may be used as a CaO source in the hot metal preliminary dephosphorization process, and the remaining part of the converter slag may be used for the reduction process in the first process.

  The blast furnace hot metal discharged from the blast furnace is received by a torpedo car, the blast furnace hot metal contained in the torpedo car is subjected to desiliconization treatment and preliminary dephosphorization treatment, and then the blast furnace hot metal is transferred to the hot metal ladle and the blast furnace in the hot metal ladle. The molten iron is subjected to mechanical stirring desulfurization treatment, the blast furnace hot metal after this desulfurization treatment is charged into the converter, decarburized and refined in the converter, and thus the molten steel is melted from the blast furnace molten iron. The present invention was applied in the steelmaking process. Table 3 shows examples of chemical components of the blast furnace hot metal and molten steel from the blast furnace tapping to the end of converter decarburization refining.

As shown in Table 3, the blast furnace hot metal after desiliconization and dephosphorization contains 0.05% by mass of phosphorus, which is higher than the phosphorus concentration level (0.025% by mass or less) of the product, The converter slag generated by the converter decarburization refining using this blast furnace hot metal contains about 1.5% by mass of phosphorus (about 3.4% by mass with P ₂ O ₅ ). When this steelmaking slag is reused as a CaO source in the sintering process, enrichment of phosphorus in the blast furnace hot metal occurs. Therefore, a test (Invention Example 1) for applying the present invention to this converter slag was conducted.

  250 ton converter slag, 50 ton blast furnace hot metal, and coke as reducing agent are charged into a three-phase AC arc furnace, an arc is generated to heat the converter slag and coke, and the converter slag The reduction treatment of was carried out. Blast furnace hot metal promotes the reduction of steelmaking slag by heating the steelmaking slag in the presence of molten metal in the furnace in advance, and at the same time, rapidly takes in the phosphorus-containing iron produced by the reduction of the steelmaking slag, It was inserted for the purpose of promoting separation from steelmaking slag. The temperature of the blast furnace hot metal was 1300 ° C. About 100 tons of high phosphorus hot metal including the previously charged blast furnace hot metal was obtained by the reduction treatment for 30 minutes. Table 4 shows the conditions for the reduction treatment, and Table 5 shows the composition of the steelmaking slag before and after the reduction treatment.

In addition, a test (Invention Example 2) was performed in which the present invention was applied to a mixture of dephosphorization slag generated in the hot metal preliminary dephosphorization treatment and the converter slag (mixing ratio = 1: 1). The composition of the converter slag is the same as that of the converter slag used in Example 1 of the present invention (see Table 5). The composition of the dephosphorization slag is CaO: 22 mass%, SiO ₂ : 18 mass%, P: They were 2.4% by mass, FexO: 28% by mass, MgO: 5.2% by mass, and MnO: 4.1% by mass.

  In the above arc furnace, 250 tons of a mixture of converter slag and dephosphorization slag, 50 tons of blast furnace hot metal, and coke as a reducing agent are charged, an arc is generated to heat the mixed slag and coke, Reduction treatment of mixed slag was performed. Blast furnace hot metal promotes the reduction of mixed slag by heating the molten slag in the presence of molten metal in the furnace in advance, and at the same time, rapidly takes in the phosphorus-containing iron produced by the reduction of the mixed slag, It is inserted for the purpose of promoting separation from the mixed slag.

  The furnace slag melted earlier than in the first invention example, and a high phosphorus hot metal of about 100 tons was obtained by the reduction treatment for 25 minutes together with the blast furnace hot metal charged in advance. The conditions for the reduction treatment are the same as in Table 4 described above. Table 5 described above shows the composition of the mixed slag before and after the reduction treatment.

  In both Invention Example 1 and Invention Example 2, the obtained high phosphorus hot metal was discharged from the arc furnace to the hot metal ladle, and then about 200 tons of converter slag remaining in the furnace was discharged into the slag pot. In the present invention example 1, the chemical components of the obtained high phosphorus hot metal were: carbon: 4.3% by mass, silicon: 0.01% by mass, manganese: 2.2% by mass, phosphorus: 3.0% by mass, sulfur : 0.05% by mass, and in Example 2 of the present invention, carbon: 4.3% by mass, silicon: 0.01% by mass, manganese: 3.1% by mass, phosphorus: 4.5% by mass, sulfur: 0.00%. It was 05 mass%. Invention Example 2 had a higher phosphorus concentration, but the others were equivalent.

  P / Fe of the phosphorus-containing steelmaking slag is 0.5 to 7.5% by mass in terms of P concentration, but in this example, it is diluted to a concentration of about ½ using blast furnace hot metal. In this case, the P concentration is 0.25 to 3.75% by mass, and the phosphorus concentration is within this range, which is consistent with the past results. The high phosphorus hot metal was dephosphorized using the dephosphorization equipment shown in FIG. Table 6 shows the dephosphorization treatment conditions performed on the high phosphorus hot metal in Invention Example 1 and Invention Example 2.

  By this dephosphorization treatment, the phosphorus concentration of the high phosphorus hot metal was reduced to 0.1% by mass in both inventive examples 1 and 2. Table 7 shows the chemical composition of the high phosphorus hot metal before and after the dephosphorization treatment.

The high phosphorus hot metal after the dephosphorization treatment was mixed with the blast furnace hot metal, and the mixed hot metal was subjected to desiliconization / dephosphorization treatment, and then charged into the converter through a desulfurization treatment step. In the converter, ordinary refining was performed to produce molten steel of a predetermined component. Further, by this dephosphorization treatment of the high phosphorus hot metal, both of the inventive examples 1 and 2 were CaO: 62 mass%, SiO ₂ : 2.2 mass%, P: 28 mass%, Fe _x O: 2. A dephosphorized slag of 8% by mass, MgO: 4% by mass, and MnO: 0.8% by mass was obtained. This dephosphorization slag could be used as a phosphorus fertilizer.

  On the other hand, the converter slag after the reduction treatment is cooled, and then used as a CaO source for the iron making agent in the iron ore sintering step, and the manufactured sintered ore is charged into the blast furnace as the iron source, Blast furnace hot metal was produced. The phosphorus concentration of the blast furnace hot metal melted was about 0.1% by mass, and there was no problem at all.

  On the other hand, when the converter slag generated in the steelmaking process is recycled as it is as a CaO source of sintered ore, the phosphorus concentration in the hot metal discharged from the blast furnace becomes high, and in the preliminary dephosphorization treatment of the hot metal The basic unit of the dephosphorizing agent (oxygen source and CaO-based flux) and the amount of dephosphorizing slag generated increased 1.5 times, and the productivity was reduced by 20%.

  In the present invention, about 80% by mass of iron contained in the converter slag was recovered, which was almost equivalent to the case where the converter slag was directly recycled as a CaO source of sintered ore. .

DESCRIPTION OF SYMBOLS 1 Dephosphorization processing equipment 2 High phosphorus hot metal 3 Dephosphorization slag 4 Hot metal ladle 5 Bogie 6 Top blowing lance 7 Injection lance

Claims (8)

  Steelmaking slag containing phosphorus generated in the steelmaking refining process is reduced using a reducing agent containing at least one of carbon, silicon, and aluminum, and iron oxide and phosphorous oxide in the steelmaking slag are removed. A first step of reducing and recovering molten iron-containing molten iron from steelmaking slag, and a second step of recycling the steelmaking slag from which iron oxide and phosphorous oxide have been removed as a CaO source in the ironmaking step or steelmaking step. The process and the phosphorus-containing molten iron recovered by the reduction treatment are dephosphorized using a CaO-based flux not containing fluorine until the phosphorus concentration in the phosphorus-containing molten iron becomes 0.1 mass% or less, and CaO A third step of concentrating phosphorus in the system flux, and a blast furnace molten iron obtained from the blast furnace using the phosphorus-containing molten iron having a phosphorus concentration of 0.1% by mass or less subjected to the dephosphorization treatment as an iron source Fourth and having a step, a method for recovering iron and phosphorus from steelmaking slag to mix.   The method for recovering iron and phosphorus from steelmaking slag according to claim 1, wherein slag generated in decarburization and refining of hot metal in a converter is subjected to a reduction treatment in the first step.   The mixture of the slag generated in the decarburization and refining of the hot metal in the converter and the slag generated in the preliminary dephosphorization of the hot metal is used for the reduction treatment in the first step. A method for recovering iron and phosphorus from the described steelmaking slag.   The method for recovering iron and phosphorus from steelmaking slag according to any one of claims 1 to 3, wherein the phosphorus-containing molten iron is hot metal containing 3 mass% or more of carbon.   The method for recovering iron and phosphorus from steelmaking slag according to any one of claims 1 to 4, wherein the reduction treatment in the first step is performed in the presence of blast furnace hot metal.   The steelmaking slag according to any one of claims 1 to 5, wherein a recycling destination of the steelmaking slag in the second step is an iron ore sintering step or a hot metal production step in a blast furnace. Recovery method of iron and phosphorus from slag.   The recycling destination of the steelmaking slag in the second step is a hot metal dephosphorization step or a hot metal decarburization refining step in a converter, according to any one of claims 1 to 5. To recover iron and phosphorus from steelmaking slag.   The iron from the steelmaking slag according to any one of claims 1 to 7, wherein the CaO-based flux that concentrates phosphorus used in the third step is used as a phosphorus resource. Phosphorus recovery method.

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