JP5531536B2 - Method for recovering iron and phosphorus from steelmaking slag - Google Patents

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 preliminary dephosphorization treatment of hot metal.

  Due to the iron ore component, the hot metal melted in the blast furnace (referred to as “blast furnace hot metal”) contains phosphorus (P). Since phosphorus is a harmful component for steel materials, conventionally, phosphorus removal treatment has been 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 the 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 (referred to as “phosphorus-containing steelmaking slag”) generated by dephosphorization and decarburization and refining of hot metal in a converter has been conventionally excluded from the steel manufacturing process as a civil engineering material. The phosphorus and iron in the steel slag containing phosphorus were not recovered.

  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 by converter decarburization refining using hot metal that has been subjected to preliminary dephosphorization treatment (slag generated in converter decarburization refining is referred to as “converter slag”) has an iron oxide content and a CaO content. Since it is high and has a low phosphorus content, it is recycled to a blast furnace through a sintering process as an iron source and a CaO source for a slagging agent.

  Slag generated in converter decarburization and refining using pre-dephosphorized hot metal (also called “dephosphorized hot metal”), especially dephosphorized hot metal pre-dephosphorized to the phosphorus concentration level of steel products. Contains almost no phosphorus, and there is no need to worry about an increase in phosphorus concentration in hot metal by recycling to blast furnace. However, the slag generated during preliminary dephosphorization, hot metal that has not been preliminarily dephosphorized (also referred to as “normal hot metal”), or even if it has been preliminarily dephosphorized, the phosphorus concentration has dropped to the phosphorus concentration level of the steel product. When the slag containing phosphorus is recycled to the blast furnace, such as the converter slag generated in the decarburization and refining of the converter using no dephosphorizing hot metal, phosphorus recycled to the blast furnace as oxide is It is reduced to increase the phosphorus content of the hot metal, resulting in a vicious circle in which the load of dephosphorization from the hot metal is increased. Therefore, various proposals have been made regarding the recycling of steelmaking slag containing phosphorus in order to prevent the pickup of phosphorus.

  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.

  Further, Patent Document 3 discloses that a dephosphorization slag produced by a dephosphorization treatment of hot metal or molten steel using a slagging agent mainly composed of an alkali metal carbonate is treated with water and carbon dioxide gas to obtain alkali metal phosphorus. A technique is disclosed in which an extract containing an acid salt 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, the converter slag, which is phosphorus-containing slag, is mixed with the same amount of blast furnace slag as the converter slag. However, in recent years, the blast furnace slag is not a mere industrial by-product, but a viewpoint such as CO ₂ reduction. Therefore, it is economically disadvantageous to use such blast furnace slag for dilution of 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.

  In view of such circumstances, the present inventors, at the time of recycling steelmaking slag containing phosphorus such as dephosphorization slag and converter slag, recovered phosphorus and iron at low cost from the steelmaking slag, and recovered phosphorus and We have been researching the recovery of iron and phosphorus from steelmaking slag, which can effectively use iron as a resource. And, as Japanese Patent Application No. 2008-331686, “a steelmaking slag containing phosphorus generated in the steelmaking refining process is reduced using a reducing agent, and the iron oxide and the phosphorous oxide in the steelmaking slag are in a molten state containing phosphorus. The first step of reducing and recovering from steelmaking slag as iron and steelmaking slag from which iron oxide and phosphorous oxide have been removed are used as a CaO source in the iron ore sintering process, and the produced sintered ore is used as a blast furnace. Until the phosphorus concentration in the phosphorus-containing molten iron becomes 0.1% by mass or less using the CaO-based flux not containing fluorine. A third step of dephosphorizing and concentrating phosphorus in the CaO-based flux, and a phosphorus-containing molten iron having a phosphorus concentration of 0.1% by mass or less subjected to the dephosphorization treatment as an iron source from a blast furnace Got caught A fourth step of mixing the hot metal, and filed a recovery process "of iron and phosphorus from steelmaking slag.

  The above invention is a very effective technique from the viewpoint of effective use of resources and reduction of refining load. However, when iron oxide and phosphorous oxide are converted to phosphorus-containing molten iron by reduction treatment, there are cases in which, after cooling, slag and phosphorus-containing iron are in close contact with each other, making it difficult to separate them. In such a case, a crushing process or the like is required to separate the two, and additional energy is required.

  Based on this result, the present inventors came to the idea that there is room for further improvement in resource efficiency including energy, and further examined the recovery of iron and phosphorus from steelmaking slag.

  The present invention has been made in view of such circumstances. The object of the present invention is to recycle phosphorus and iron from steelmaking slag when recycling steelmaking slag containing phosphorus such as dephosphorization slag and converter slag. An object of the present invention is to provide a method for recovering iron and phosphorus from steelmaking slag, which can provide a method for separating and recovering inexpensively and easily, and that can effectively use the recovered phosphorus and iron as resources.

The present inventors examined a method for drastically improving the separation and recovery efficiency of phosphorus-containing iron and slag after reduction treatment. As a result, the properties of the steel slag is subjected to a reduction treatment, in particular by controlling the basicity of the steel slag (mass% CaO / mass% SiO ₂₎ to a particular range, it is significantly improved separation and recovery I found out.

The present invention has been made on the basis of the above knowledge, and the method for recovering iron and phosphorus from steelmaking slag according to the first invention is characterized in that the steelmaking slag containing phosphorus generated in the steelmaking refining process is treated with basicity ( The preparation step of preparing so that the mass% CaO / mass% SiO ₂ ) is 1.7 or more and 2.1 or less, and the steelmaking slag whose basicity is adjusted, containing one or more of carbon, silicon, and aluminum A reduction step of reducing iron oxide and phosphorous oxide in the steelmaking slag as molten phosphorus-containing molten iron from the steelmaking slag by using a reducing agent, and reducing steelmaking slag and phosphorus-containing molten iron And a cooling step of pulverizing the steelmaking slag after the reduction treatment.

  In the method for recovering iron and phosphorus from steelmaking slag according to the second invention, in the first invention, the steelmaking slag containing phosphorus generated in the steelmaking refining process is used in the decarburizing and refining treatment of hot metal in a converter. It is characterized by containing slag generated in the preliminary dephosphorization treatment of the generated slag and / or hot metal.

  In the method for recovering iron and phosphorus from steelmaking slag according to the third invention, in the first invention, as a steelmaking slag containing phosphorus generated in the steelmaking refining process, in the decarburization refining treatment of hot metal in a converter Using only two types of slag generated in the preliminary dephosphorization treatment of the generated slag and hot metal, the basicity is adjusted by adjusting the mixing ratio of the two types of slag in the basicity adjustment step. .

  The method for recovering iron and phosphorus from the steelmaking slag according to the fourth invention is the method of recovering iron and phosphorus from the steelmaking slag according to any one of the first to third inventions, and further, after the cooling step, further magnetically sorted to powder the molten iron containing phosphorus. It has a separation / collection process for separating and collecting steelmaking slag.

  The method for recovering iron and phosphorus from the steelmaking slag according to the fifth invention is the method according to any one of the first to third inventions, wherein, after the cooling step, a sieve having a mesh size of 5 mm or more and 15 mm or less. It is characterized by having a separation / recovery step of separating and recovering phosphorus-containing molten iron and powdered steelmaking slag by sieving.

  The method for recovering iron and phosphorus from the steelmaking slag according to the sixth invention is the method of recovering steelmaking slag from the fourth or fifth invention, wherein the iron oxide and the phosphorous oxide are further removed after the separation and recovery step. Recycling the iron-containing process as a CaO source and the phosphorus-containing molten iron recovered by the reduction treatment using a CaO-based flux not containing fluorine, the phosphorus concentration in the phosphorus-containing molten iron becomes 0.1% by mass or less. And the process of concentrating phosphorus in the CaO-based flux, and the phosphorus-containing molten iron having a phosphorus concentration of 0.1% by mass or less, which has been subjected to the dephosphorization process, discharged from the blast furnace as an iron source. And mixing with the molten iron produced.

  The method for recovering iron and phosphorus from steelmaking slag according to the seventh invention is the method of recovering iron and phosphorus from the steelmaking slag according to the sixth invention, wherein the steelmaking slag from which the iron oxide and phosphorous oxide have been removed is used in the iron ore sintering process or hot metal in a blast furnace. It is characterized by recycling as a CaO source in the manufacturing process.

  The method for recovering iron and phosphorus from steelmaking slag according to the eighth invention is characterized in that, in the sixth or seventh invention, the CaO-based flux enriched with phosphorus is recovered as a phosphoric acid resource raw material.

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

  The method for recovering iron and phosphorus from steelmaking slag according to the tenth invention is characterized in that, in any one of the first to ninth inventions, the reduction treatment is performed in the presence of hot metal discharged from a blast furnace. And

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. From the steelmaking slag, the iron oxide and phosphorous oxide in the steelmaking slag are reduced and separated as phosphorus-containing molten iron, and recovered as phosphorus-containing iron after cooling. (CaO / mass% SiO ₂ ) is adjusted to 1.7 or more and 2.1 or less, so that the main component of the steelmaking slag after the removal of the iron oxide and phosphorous oxide is 2CaO—SiO ₂ , and this is a low temperature when allowed to cool. When it reaches the zone, it undergoes a phase transformation, and it collapses into a powder form by this phase transformation. As a result, powdered slag and massive phosphorus-containing iron can be easily separated, and the mixture of reduced slag and phosphorus-containing iron can be separated without any special treatment such as crushing treatment. -Recovery becomes possible, and it is realized that iron and phosphorus contained in steelmaking slag are each effectively used as a resource at low energy costs.

It is a figure which shows the relationship between the basicity of steelmaking slag, and the mass ratio which the particle | grains less than 1 mm in particle diameter in the steelmaking slag after cooling account. It is a figure which shows the example of the particle size distribution of the steelmaking slag after pulverization.

  Hereinafter, the present invention will be described in detail.

  The present inventors have found that the dephosphorization slag generated during the preliminary dephosphorization treatment of the hot metal, and the phosphorus concentration after the predephosphorization treatment compared with the phosphorus concentration level of the steel product even though the hot metal or the predephosphorization treatment is performed. Steelmaking slag containing phosphorus, such as converter slag generated during decarburization and refining of converters using high dephosphorizing hot metal, and iron ore sintering processes and blast furnaces as a source of CaO for ironmaking agents In recycling process in hot metal manufacturing process in Japan, it was studied to eliminate the influence of phosphorus contained in this phosphorus-containing steelmaking slag on hot metal.

  The converter slag generated during the decarburization and refining of hot metal, which has been pre-dephosphorized to the phosphorus concentration level of steel products, is produced in the blast furnace through the iron ore sintering process without picking up the phosphorus concentration of hot metal. Recycled as a glaze. 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 contains iron in the form of FeO or Fe ₂ O ₃ (hereinafter collectively referred to as “FeO _x ”), and these iron oxides contain oxygen. Since the affinity is equivalent to phosphorus, it has been found that when phosphorus-containing steelmaking slag is reduced with carbon, silicon, aluminum, etc., FeO _x in the steelmaking slag is reduced simultaneously.

  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. In other words, if the iron produced by reduction is in a molten state, the molten iron and slag are separated, and the phosphorus produced in the molten iron is dissolved (the produced molten iron is “phosphorus-containing molten iron” It was found that the separation of phosphorus from the steelmaking slag was also accelerated.

  In this case, the lower the melting point of the produced phosphorus-containing molten iron, the more the separation of the phosphorus-containing molten iron and slag is promoted. Therefore, carbon is dissolved in the produced phosphorus-containing molten iron to obtain phosphorus-containing molten iron. It has also been found preferable to produce hot metal containing phosphorus. Specifically, when the carbon concentration is 3% by mass or more, the liquidus temperature of the molten iron becomes 1300 ° C. or less, and therefore it is preferable to ensure the carbon concentration of the produced phosphorus-containing molten iron of 3% by mass or more. I understood that. In order to dissolve carbon in the phosphorus-containing molten iron to be produced, carbon is used as a reducing agent, or when silicon or aluminum is used as a reducing agent, it is produced by coexisting carbon with steelmaking slag. The molten iron is carburized into natural hot metal (this hot metal is called “high phosphorus hot metal” to distinguish it from “blast furnace hot metal”).

  In addition, during the reduction treatment, it is possible to simultaneously charge the blast furnace hot metal. Ingots in steelmaking slag may have a low carbon content and have a relatively high melting point, but since molten metal can be maintained at a relatively low temperature by adding molten iron at the same time, it must flow in the reaction vessel. Even when granular iron having a high melting point is present, it can be efficiently separated as molten iron by adhering and coalescing with the blast furnace hot metal. In other words, it has been found that it is preferable to perform reduction treatment of phosphorus-containing steelmaking slag by charging the blast furnace hot metal under conditions that allow preparation of the blast furnace hot metal.

  When the reduction reaction is effectively promoted, the phosphorus-containing steelmaking slag is composed of a complex oxide (steelmaking slag after reduction treatment) in which iron oxide and phosphorous oxide are removed from the composition before the reduction treatment, and a large amount. It is divided into phosphorus-containing molten iron containing phosphorus. In order to separate and recover the reduced iron and phosphorus, it is necessary to separate the phosphorus-containing molten iron from the steelmaking slag after the reduction treatment.

  When a large amount of phosphorus-containing molten iron is produced, it is relatively easy to separate the two. However, when phosphorus-containing steelmaking slag is reduced, the production of phosphorus-containing molten iron with respect to the amount of slag remaining as a residue. The amount is not large, it is difficult to separate only the phosphorus-containing molten iron by hot water, and when both the high-temperature molten state after the reduction treatment is discharged into a slag pot or slag yard and cooled, In many cases, phosphorus-containing iron and steelmaking slag after the reduction treatment coexist, and in such a case, a process such as a crushing treatment is required in order to separate the two. Actually, the converter slag is cooled and then crushed, and then magnetically selected to collect the metal that is mixed in the converter slag.

  In order to simplify the process, the present inventors have considered omitting a process for separating both the crushing process and the like. While studying various reduction conditions and slag composition, when a certain condition is reached, the steelmaking slag after reduction treatment is agglomerated immediately after cooling from a high temperature state when cooling after reduction treatment. On the other hand, it has been found that there is a case where it collapses into powder as the cooling progresses, and the phosphorus-containing iron and the steelmaking slag after reduction can be easily separated.

Fig. 1 shows the basicity (mass% CaO / mass% SiO ₂ ) of steelmaking slag when the steelmaking slag after reduction treatment is allowed to cool to room temperature in the atmosphere, and particles less than 1 mm in the steelmaking slag after cooling. The relationship with the mass ratio of is shown. In addition, the particle | grains less than 1 mm in steelmaking slag are what separated the whole amount of steelmaking slag after cooling with the sieve whose mesh size is 1.0 mm, and the basicity of steelmaking slag is 2 or more types of steelmaking slag. When steel slag, silica sand, and the like are mixed, the average value is obtained by summing the values obtained by multiplying the basicity and the mixing ratio.

  As shown in FIG. 1, when the basicity is 1.6 or less, most of the steelmaking slag after the reduction treatment is massive, and particles less than 1 mm are hardly generated in an uncrushed state. On the other hand, when the basicity exceeds 2.5, particles slightly less than 1 mm are generated, but most of them are lumps. On the other hand, when the basicity is in the range of 1.7 or more and 2.1 or less, it was found that the portion exceeding 80% by mass is occupied by particles less than 1 mm. Table 1 shows an example of component analysis of the steelmaking slag at this time.

It was found that the slag of less than 1 mm after the reduction treatment contained almost no iron and phosphorus, and most was a steelmaking slag that was reduced. That is, by adjusting the basicity of the phosphorus-containing steelmaking slag to be reduced to 1.7 or more and 2.1 or less, the main component of the steelmaking slag after the reduction treatment is 2CaO—SiO ₂ , which is released in the atmosphere. When it reaches a low temperature range when it is cold, it undergoes a phase transformation, disintegrates and pulverizes, and after the reduction treatment, the mixture of steelmaking slag and phosphorus-containing iron after the reduction treatment is not subjected to grinding treatment. It was found that steelmaking slag and phosphorus-containing iron can be separated.

The present invention has been made based on the above test results. In recovering iron and phosphorus from phosphorus-containing steel slag, the basicity (mass% CaO / mass% SiO ₂ ) of the phosphorus-containing steel slag is 1. The preparation process prepared so that it may become 7 or more and 2.1 or less, and the phosphorus containing steelmaking slag which adjusted basicity are reduce-processed using the reducing agent containing 1 or more types in carbon, silicon, and aluminum. A reduction step of reducing iron oxide and phosphorous oxide in phosphorus-containing steelmaking slag from phosphorus-containing steelmaking slag as phosphorus-containing molten iron in a molten state, and reducing treatment by allowing the steelmaking slag and phosphorus-containing molten iron after reduction to cool. And a cooling step of pulverizing the later steelmaking slag. In particular, the steelmaking slag and phosphorus-containing molten iron after the reduction treatment are preferably allowed to cool from the reduction treatment container and allowed to cool in the atmosphere.

There is no particular limitation on the method for preparing the basicity of the phosphorus-containing steelmaking slag before the reduction treatment so as to be 1.7 or more and 2.1 or less. For example, it occurs in the decarburization and refining treatment of hot metal in a converter. The slag generated in the preliminary dephosphorization treatment of the molten slag and / or hot metal may be contained. Specifically, a phosphorus-containing steelmaking slag having a basicity lower than 1.7 may be added and mixed with a raw material having a high CaO content, and conversely, a phosphorus containing a basicity higher than 2.1. For steelmaking slag, raw materials having a high SiO ₂ content may be added and mixed. In this case, it may be melted and homogenized, but homogenization is not necessarily required as long as it is mixed in a solid state.

  However, in order to efficiently recover iron and phosphorus, the raw materials used must contain iron oxides and phosphorous oxides, and the raw materials with sensible heat can be dissolved and reduced more efficiently. Therefore, only two types of slag generated in the decarburization and refining treatment of hot metal in the converter and slag generated in the preliminary dephosphorization treatment of hot metal are used, and these two types of slag are used in the basicity preparation step. It is preferable to adjust the basicity by adjusting the mixing ratio. That is, as the phosphorus-containing steelmaking slag having a basicity higher than 2.1, the converter slag containing phosphorus, which is generated in the decarburization refining process in the converter in the steelmaking process, is used, and the basicity is 1.7 or more. It is preferable to use the dephosphorization slag generated in the hot metal preliminary dephosphorization process in the steelmaking process as the low phosphorus-containing steelmaking slag, and to adjust the mixing ratio by adjusting these mixing ratios without using other raw materials. . Of course, the converter slag or the dephosphorization slag may be used alone without being mixed when the basicity is 1.7 or more and 2.1 or less.

  Moreover, in this invention, in order to collect | recover iron and phosphorus and steelmaking slag after a reduction process as a CaO source, after a cooling process, phosphorus containing iron and powdered steelmaking slag are fractionated and collect | recovered. As this separation / recovery method, it is preferable to use magnetic separation. If the separation between the two has not progressed, even if the magnetic separation is carried out, the slag is attracted at the same time, and the quality of the phosphorus-containing iron is lowered, but the slag part after the reduction treatment is pulverized. As a result, it is possible to easily and reliably separate and collect the magnetized product (phosphorus-containing iron) and the non-magnetized product (steel slag after reduction).

  In this case, a sieving method using a sieve can be applied instead of the magnetic separation. The size of the phosphorus-containing iron varies depending on the conditions of the reduction treatment but exceeds 15 mm. On the other hand, the particle size distribution of the steelmaking slag to be pulverized does not change and the particle size is extremely fine. As shown in FIG. 2, the particle size distribution of the steelmaking slag after pulverization has an average particle size of less than 20 μm and a maximum particle size of about 200 μm. Therefore, if the sieve has an opening size exceeding the maximum particle size, it can be separated and collected. However, if the opening size is small enough to be slightly larger than the maximum particle size, the sieving speed is slow and efficient processing cannot be performed, and clogging is likely to occur. Therefore, the opening size is 5 mm. It is preferable to use a sieve having a range of 15 mm or less.

  The steelmaking slag from which iron oxide and phosphorous oxide have been separated and recovered contains CaO at a high concentration, and can be used as a substitute for the CaO source. In particular, since it is a powder and contains almost no phosphorus, it is desirable to use it as a CaO source used in the iron ore sintering process from the viewpoint of total energy considering the transportation of materials. Since the produced ore is charged into the blast furnace, the steelmaking slag is recycled in the hot metal production process in the blast furnace. However, since the steelmaking slag to be recycled has phosphorus removed, The hot metal produced does not have a phosphorus concentration pickup and does not increase the load of dephosphorization in the steelmaking process.

  On the other hand, the recovered phosphorus-containing iron has a high phosphorus concentration and is difficult to use as an iron source as it is. Therefore, in the present invention, the phosphorus-containing iron is further separated into an iron portion and a phosphorus portion. By separating the iron part and the phosphorus part, it is possible to effectively use both.

  For example, the chemical components of phosphorus-containing iron containing carbon (= high phosphorus hot metal) are: carbon: 4.3% by mass, silicon: 0.01% by mass, manganese: 2.2% by mass, phosphorus: 3.0 Since the phosphorus-containing iron has an extremely high phosphorus concentration as described above, the phosphorus-containing iron is subjected to a dephosphorization treatment so that slag having a high phosphorus concentration can be obtained. It becomes possible to separate into iron having a low phosphorus concentration.

The method for dephosphorizing phosphorus-containing iron can be performed in accordance with a method generally used in the preliminary dephosphorization treatment of blast furnace hot metal. In other words, the recovered phosphorus-containing iron is heated and melted in an arc furnace or induction furnace, preferably carburized to increase the carbon concentration, and oxygen source such as oxygen gas or iron ore is dephosphorized in this phosphorus-containing molten iron. In addition to supplying by spraying or injecting as an agent, a CaO-based flux is added and oxidized by oxygen in an oxygen source for supplying phosphorus in phosphorus-containing molten iron to P ₂ O _5, and this P ₂ O ₅ is converted into CaO. It is a method of absorbing and fixing to a system flux and dephosphorizing.

  Since the molten iron after the dephosphorization treatment is mixed with the blast furnace hot metal and recycled as an iron source, it is preferable to carry out the dephosphorization treatment until the phosphorus concentration becomes equal to or less than 0.1% by mass as the blast furnace hot metal. Conversely, the phosphorous oxide is concentrated at a high concentration in the CaO-based flux by performing the dephosphorization treatment until the phosphorus concentration in the molten iron becomes 0.1% by mass or less.

  A CaO-based flux enriched with a high concentration of phosphorous oxide can be used as a substitute for phosphate ore, which has almost no resources in Japan, that is, as a phosphate resource raw material.

  Incidentally, it is known that the CaO-based flux used for the dephosphorization treatment is accelerated by the addition of about 5% by mass of a fluorine source such as fluorite to promote the hatching of CaO and the dephosphorization reaction. In the present invention, it is assumed that the CaO-based flux (dephosphorization slag) after the dephosphorization treatment is used as, for example, a phosphorus fertilizer. In this case, fluorine is eluted from the phosphorus fertilizer (dephosphorization slag) into the soil. However, since the fluorine elution value may be a problem with respect to the soil environment standard, it is preferable to carry out the dephosphorization treatment using a CaO-based flux not containing fluorine in the present invention.

According to the present invention having such a configuration, the dephosphorization slag generated by the preliminary dephosphorization treatment of the hot metal, or the converter slag generated by the converter decarburization refining using the normal hot metal or the dephosphorization hot metal that is not sufficiently dephosphorized. From the steelmaking slag containing phosphorus such as iron oxide and phosphorous oxide in the steelmaking slag, reduced and separated as phosphorus-containing molten iron, and recovered as phosphorus-containing iron after cooling, the steelmaking slag during the reduction treatment Since the basicity (mass% CaO / mass% SiO ₂ ) is adjusted to 1.7 or more and 2.1 or less, the main component of the steelmaking slag after the iron oxide and phosphorous oxide are removed is 2CaO—SiO ₂ , This causes a phase transformation when it reaches a low temperature range when it is allowed to cool in the atmosphere, and this phase transformation causes the powder to collapse. As a result, powdered slag and massive phosphorus-containing iron can be easily separated and recovered. Can be reduced Separation is possible without special treatment such as crushing of the mixture of steelmaking slag and phosphorus-containing iron afterwards, and iron and phosphorus contained in steelmaking slag can be used effectively as resources for low energy costs. Is realized.

  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 steel 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.

  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. Steelmaking where the hot metal is desulfurized using a mechanical stirring desulfurization device, the blast furnace hot metal after the desulfurization treatment is loaded into the converter, and decarburization refining is performed in the converter, and the molten steel is melted from the blast furnace hot metal. In the process, the present invention was applied.

As the phosphorus-containing steelmaking slag for which iron and phosphorus are to be recovered, converter slag generated by converter decarburization refining using normal hot metal or dephosphorized hot metal with insufficient dephosphorization is selected, and the base of this converter slag is selected. The degree (mass% CaO / mass% SiO ₂ ) was prepared using dephosphorization slag, silica sand and fly ash generated by the preliminary dephosphorization treatment of hot metal. Table 2 shows the composition of the main components of the raw materials used.

  To 100 ton converter slag, dephosphorization slag, silica sand and fly ash are added so that the basicity becomes the target basicity to make a mixture and charged into the arc furnace together with coke as a reducing agent to generate an arc. The raw material charged in this manner was heated and melted for reduction treatment. After the reduction treatment for 30 minutes, the entire amount charged was discharged from the furnace, discharged to a cooling yard and allowed to cool in the atmosphere. After cooling to room temperature, it was recovered with a shovel car, and the recovered slag mixed with phosphorus-containing iron was magnetically sorted and separated into slag and phosphorus-containing iron.

  Table 3 shows the basicity of the recovered slag and the metal separation rate without crushing treatment. Here, the metal separation rate is obtained by calculating the iron content generated by reduction from the T.Fe value in the raw material used before the reduction treatment, and the phosphorus content recovered by magnetic sorting with respect to the mass of the iron content determined by the calculation. It is the ratio of the mass of iron. A higher ratio means that the slag after reduction is pulverized and phosphorus-containing iron is recovered. T.Fe is the total iron content of all iron oxides in raw materials used such as converter slag.

  As in test No. 5, the composition of a general converter slag was hardly powdered, and the phosphorus-containing iron could not be separated from the slag without crushing treatment. Further, as in Test No. 1, with the composition of dephosphorized slag, the recovery rate of phosphorus-containing iron was only about 40% by mass without crushing treatment. On the other hand, in the present invention examples of tests No. 2, 3, 6 and 7 in which the basicity was adjusted, the recovery rate of phosphorus-containing iron was 67 to 87% by mass. Most of them were recovered.

  In Test Nos. 1, 4, and 5, since it was necessary to separate the iron-containing iron and the slag component by crushing the steelmaking slag after reduction, the test was interrupted at this stage.

  On the other hand, in the inventive examples of Test Nos. 2, 3, 6 and 7, the recovered powdered slag after the reduction treatment was used as a CaO source for a fossilizing agent in the sintering process of iron ore. The ore was charged into a blast furnace as an iron source to produce blast furnace hot metal. The phosphorus concentration of the produced blast furnace hot metal was about 0.1% by mass, and there was no problem at all. In addition, when the converter slag generated in the normal steelmaking process is recycled as it is as a CaO source in the sintering process, the phosphorus concentration of the hot metal discharged from the blast furnace becomes high, and dephosphorization in the preliminary dephosphorization treatment of the hot metal Since the basic unit of the agent (oxygen source and CaO-based flux) and the amount of dephosphorization slag generated are about 1.5 times and the productivity is reduced by about 20%, the productivity is extremely improved by applying the present invention. It was confirmed to be good.

  In addition, typical components of phosphorus-containing iron recovered in the inventive examples of Test Nos. 2, 3, 6, and 7 are carbon: 4.5% by mass, silicon: 0.01% by mass, manganese: 2. 5% by mass, phosphorus: 3.0% by mass, and sulfur: 0.05% by mass, and it was found that the carbon concentration was high and recovered in a hot metal (high phosphorus hot metal) state.

This high phosphorus hot metal is heated and melted in an arc furnace, the molten high phosphorus hot metal is poured into a ladle, and the high phosphorus hot metal in the ladle is subjected to preliminary dephosphorization treatment on the blast furnace hot metal. Using a treatment facility, dephosphorization was performed using oxygen gas and iron ore as an oxygen source, and using a CaO-based flux not containing fluorine as a CaO-based flux for absorbing P ₂ O ₅ . By this dephosphorization treatment, the phosphorus concentration of the high phosphorus hot metal was reduced to 0.1% by mass.

The dephosphorization slag derived from the CaO flux obtained by this dephosphorization treatment is CaO: 62% by mass, SiO ₂ : 2.2% by mass, P: 28% by mass, FeO _X : 2.8% by mass. MgO: 4% by mass, MnO: 0.8% by mass. As a result of evaluation by an official analysis method of fertilizer, it was confirmed that the soluble ferric acid had a very good fertilizer raw material characteristic of 20% by mass or more.

  The hot metal obtained by the dephosphorization treatment was mixed with the blast furnace hot metal, and the mixed hot metal was subjected to preliminary dephosphorization treatment and desulfurization treatment, and then charged into a converter and subjected to decarburization refining. The obtained molten steel was exactly the same as the molten steel produced from ordinary blast furnace hot metal, and was cast into slab slabs for thin steel sheets using a continuous casting machine.

Claims (11)

As steelmaking slag containing phosphorus generated in the steelmaking refining process, only two types of slag generated in the decarburization and refining process of hot metal in the converter and slag generated in the preliminary dephosphorization process of hot metal are used. Of the steelmaking slag by adjusting the mixing ratio of steel slag so that the basicity (mass% CaO / mass% SiO ₂ ) of the steelmaking slag is 1.7 or more and 2.1 or less, and the steelmaking slag whose basicity is adjusted. Reduction of iron oxide and phosphorous oxide in steelmaking slag from the steelmaking slag as phosphorus-containing molten iron in a molten state by reducing with a reducing agent containing one or more of carbon, silicon, and aluminum And a step of cooling the steelmaking slag after the reduction treatment and the phosphorus-containing molten iron to cool the steelmaking slag after the reduction treatment, and recovering iron and phosphorus from the steelmaking slag, Direction . The steelmaking slag from the steelmaking slag according to claim 1 , further comprising a separation / recovery step of separating and collecting the phosphorus-containing molten iron and the pulverized steelmaking slag after the cooling step. A method for recovering iron and phosphorus. After the cooling step, further comprising a separation / recovery step of separating and collecting phosphorus-containing molten iron and pulverized steelmaking slag by sieving with a sieve having an opening size in the range of 5 mm to 15 mm. The method for recovering iron and phosphorus from the steelmaking slag according to claim 1. Preparation steps for preparing steelmaking slag containing phosphorus generated in the steelmaking refining process so that the basicity (mass% CaO / mass% SiO ₂ ) is 1.7 or more and 2.1 or less, and the basicity was prepared. Steelmaking slag is reduced using a reducing agent containing one or more of carbon, silicon, and aluminum to reduce iron oxide and phosphorous oxide in steelmaking slag as molten phosphorus-containing molten iron from steelmaking slag. A reduction process, a cooling process in which the steelmaking slag and phosphorus-containing molten iron after the reduction treatment are allowed to cool to pulverize the steelmaking slag after the reduction treatment, and after the cooling process , magnetic selection is further performed to select phosphorus-containing molten iron. and having a separation and recovery step of separating and recovering the steelmaking slag obtained by powdering, and iron and a method for recovering phosphorus from steelmaking slag. Preparation steps for preparing steelmaking slag containing phosphorus generated in the steelmaking refining process so that the basicity (mass% CaO / mass% SiO ₂ ) is 1.7 or more and 2.1 or less, and the basicity was prepared. Steelmaking slag is reduced using a reducing agent containing one or more of carbon, silicon, and aluminum to reduce iron oxide and phosphorous oxide in steelmaking slag as molten phosphorus-containing molten iron from steelmaking slag. A reduction step, a cooling step in which the steelmaking slag and phosphorus-containing molten iron after the reduction treatment are allowed to cool to pulverize the steelmaking slag after the reduction treatment, and after the cooling step, the opening size is 5 mm to 15 mm. and having a range and separation and recovery step of the steel slag is separated and recovered to sieve sieved to was phosphorus-containing molten iron and powdering of the, iron and phosphorus from steelmaking slag recovery method . The steelmaking slag containing phosphorus generated in the steelmaking refining process contains slag generated in decarburization and refining treatment of hot metal in a converter and / or slag generated in preliminary dephosphorization treatment of hot metal. A method for recovering iron and phosphorus from a steelmaking slag according to claim 4 or 5. After the separation / recovery step, the step of recycling the steelmaking slag from which iron oxide and phosphorus oxide have been removed as a CaO source to the ironmaking process, and the phosphorus-containing molten iron recovered by the reduction treatment do not contain fluorine. Dephosphorization treatment using a CaO-based flux 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. And a step of mixing molten iron containing phosphorus having a phosphorus concentration of 0.1% by mass or less with molten iron discharged from a blast furnace as an iron source . A method for recovering iron and phosphorus from steelmaking slag according to item 1 . The steelmaking slag the iron oxide and phosphorus oxide has been removed, characterized by recycling as CaO source to molten iron manufacturing process in the sintering process or a blast furnace for iron ore, from steelmaking slag according to claim 7 A method for recovering iron and phosphorus. The method for recovering iron and phosphorus from steelmaking slag according to claim 7 or 8 , wherein the CaO-based flux enriched with phosphorus is recovered as a phosphoric acid resource raw material. The method for recovering iron and phosphorus from steelmaking slag according to any one of claims 1 to 9 , 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 10 , wherein the reduction treatment is performed in the presence of hot metal discharged from a blast furnace.

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