JP2013044029A - Method for recovering iron and phosphorus from steelmaking slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering phosphorus and iron from steelmaking slag, by which phosphorus and iron are inexpensively recovered from steelmaking slag containing phosphorus and the recovered phosphorus and iron are utilized as resources, when the steelmaking slag containing the phosphorus is recycled into an ironmaking process and a steelmaking process.SOLUTION: The method for recovering the iron and the phosphorus from steelmaking slag comprises: a first step in which the basicity (CaO/SiO) of the whole objective material to be subjected to reduction treatment and including the steelmaking slag is adjusted so as to fall within the range of 1.0-3.0, then the iron oxide in the slag is reduced with a carbon-containing reducing agent at 1,100-1.300°C to obtain reduced iron; a second step in which the slag with the iron oxide quantity decreased in the first step, is reduced with the carbon-containing reducing agent and phosphorus oxide in the slag is reduction-removed to a gas phase; a third step in which the slag obtained in the second step is reused as a CaO source in the ironmaking process or the steel making process; a fourth step in which the reduced iron obtained in the first step is reused as the iron source in the ironmaking process or the steelmaking process; and a fifth step in which the phosphorus reduction-removed to the gas phase in the second step is recovered with waste gas equipment and utilized as a phosphorus acid source raw material.

Description

  The present invention recovers iron and phosphorus from phosphorus-containing steelmaking slag such as preliminary dephosphorization slag of hot metal generated in the steelmaking refining process and converter decarburization refining slag, and produces steelmaking slag from which iron and phosphorus are recovered. The present invention relates to a method for recovering iron and phosphorus from steelmaking slag for recycling to a dredging process or a steelmaking process and for effectively using the recovered iron and phosphorus as resources.

Due to the iron ore component, hot metal (also referred to as “blast furnace hot metal”) melted in the blast furnace 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, phosphorus in hot metal or molten steel is generally oxidized to P ₂ O ₅ by an oxygen source such as oxygen gas or iron oxide, and then the generated P ₂ O ₅ is converted to CaO. It is removed by being fixed in the slag as the main component. When phosphorus in hot metal or molten steel is oxidized with oxygen gas, iron is also oxidized, and even when iron oxide is not used as an oxygen source, iron is also contained in the form of oxide in the slag.

By the way, due to the problem of depletion of phosphate ore and the inclusion of phosphate ore in China, the United States, etc., phosphorus resources have soared, and phosphorus in steelmaking slag generated in the steel refining process has been reviewed as a valuable phosphorus resource. Yes. However, since the phosphorus concentration in the hot metal discharged from the blast furnace is about 0.1% by mass, P ₂ in the steelmaking slag produced by the conventional general hot metal preliminary dephosphorization treatment and converter decarburization refining. O ₅ concentration is about 5% by mass at most, and there is almost no utilization place as a phosphoric acid resource, and these steelmaking slags have been discharged out of the steel manufacturing process as earthwork materials such as roadbed materials. The phosphorus and iron in the slag were not recovered. The hot metal preliminary dephosphorization treatment is a refining process in which the phosphorus in the hot metal is removed in advance before the hot metal is decarburized and refined 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 a CaO source and iron source for the ironmaking agent. Recycling to a blast furnace through an iron ore sintering process, recycling as a CaO source in a hot metal pretreatment process, and the like are performed.

  Pre-dephosphorized hot metal (also referred to as “dephosphorized hot metal”), especially converter slag generated in converter decarburization refining of dephosphorized hot metal preliminarily dephosphorized to the phosphorus concentration level of steel products, There is almost no inclusion, and there is no need to worry about the increase (pickup) of hot metal phosphorous concentration caused by recycling this slag to the 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 the phosphorus concentration after dephosphorization even if predephosphorized, In the slag containing phosphorus, such as the converter slag generated by decarburization and refining of dephosphorized hot metal not reduced to the level, phosphorus recycled in the form of oxides in the blast furnace is reduced in the blast furnace. As a result, the phosphorus content of the molten iron is increased, resulting in a vicious circle in which the load of dephosphorization from the molten iron is increased.

  Therefore, with regard to recycling of steelmaking slag containing phosphorus, especially for recycling to processes involving reductive refining, a method of removing phosphorus from steelmaking slag or in steelmaking slag in order to prevent picking up phosphorus concentration in hot metal Various proposals such as a method for recovering phosphorus have been made. In addition, in the case of recycling to oxidative refining such as preliminary dephosphorization treatment, since it already contains phosphorus, 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 smelted 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 subjected to vaporization and dephosphorization treatment. A technique for recycling to a process is disclosed.

  Patent Document 2 discloses a technique in which carbon is added to molten or semi-molten smelted slag containing phosphorus, oxygen is blown up under reduced pressure, and phosphorus in the slag is vaporized and removed. Yes.

In Patent Document 3, a molten blast furnace slag and a 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 mixture slag. the phosphorus oxide in the mixed slag is reduced and phosphorus vapor, and the sulfur in the mixed slag and SO _2, these are evaporated as a small slug of phosphorus and sulfur, recycling the slag to a blast furnace or converter technology Is disclosed.

  Patent Document 4 discloses a technique for adding a carbonaceous material to preliminary dephosphorization slag, heating to 1450 ° C. or higher and lower than 1700 ° C. to remove and recover phosphorus in the slag to the hot metal side, and regenerating the preliminary dephosphorization slag. Has been.

  Patent Document 5 discloses alkali metal phosphate by treating dephosphorization slag produced by dephosphorization of hot metal or molten steel, using water and carbon dioxide gas, using a slagging agent mainly composed of an alkali metal carbonate. A technique is disclosed in which an extract containing a 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 9-316519 A JP-A-55-97408 JP 2002-69526 A JP-A-56-22613

  However, the above prior art has the following problems.

  That is, in Patent Document 1, dephosphorization slag is recyclable after phosphorus is removed by vaporization and dephosphorization. However, recovery of vaporized and dephosphorized phosphorus is not mentioned, and from the viewpoint of securing phosphorus resources. It is not an effective recycling method. Similarly, in Patent Document 2, phosphorus cannot be recovered as a resource, and pressure reduction is necessary, resulting in high equipment costs.

  In Patent Document 3, the converter slag, which is phosphorus-containing slag, is mixed with the same amount of blast furnace slag as the converter slag, but in recent years, the blast furnace slag is not a waste but a utility value as a civil engineering / building material. It is economically disadvantageous to use such blast furnace slag for diluting converter slag.

  Patent Document 4 discloses the process up to the step of recovering phosphorus in the slag to the hot metal side, but does not mention how to treat the phosphorus recovered and concentrated in the hot metal thereafter.

  Further, Patent Document 5 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 recycle steelmaking slag containing phosphorus such as hot metal preliminary dephosphorization slag and converter slag to the ironmaking process and the steelmaking process. Steelmaking, in which phosphorus and iron can be recovered from the steelmaking slag in advance at a low cost, and the recovered phosphorus and iron can be effectively utilized as resources, respectively, in order to prevent the influence of phosphorus contained in the slag on molten iron and molten steel It is to provide a method for recovering iron and phosphorus from slag.

The gist of the present invention for solving the above problems is as follows.
(1) Steelmaking slag containing at least any one of phosphorus out of slag generated in hot metal decarburization and refining treatment of hot metal in a converter, including the steelmaking slag After adjusting the basicity ((mass% CaO) / (mass% SiO ₂ )) of the whole reduction object to be reduced to a range of 1.0 to 3.0, a temperature of 1100 to 1300 ° C. A first step of reducing the iron oxide in the steelmaking slag and recovering the reduced iron using a reducing agent containing carbon at
A second step of reducing the slag whose amount of iron oxide has been reduced by the reduction treatment of the first step using a reducing agent containing carbon, and reducing and removing phosphorous oxide contained in the slag to the gas phase; ,
A third step of recycling the slag having a reduced phosphorus content by the second step as a CaO source in the iron making step or the steel making step;
A fourth step of recycling the reduced iron recovered in the first step as an iron source in the iron making step or the steel making step;
A fifth step of recovering and removing phosphorus reduced to the gas phase in the second step as a phosphorous oxide in the exhaust gas treatment system and using it as a phosphoric acid resource raw material;
A method for recovering iron and phosphorus from steelmaking slag, comprising:
(2) In the reduction treatment of the first step, the basicity ((mass% CaO) / (mass% SiO ₂ )) of the whole reduction object is in the range of 1.0 to 3.0. The method for recovering iron and phosphorus from steelmaking slag as described in (1) above, wherein an SiO ₂ source is used.
(3) The method for recovering iron and phosphorus from the steelmaking slag according to (1) or (2) above, wherein in the second step, reduction treatment is performed at a temperature of 1350 to 1500 ° C.
(4) In the fifth step, any one of the above (1) to (3), wherein the phosphorus oxide is recovered using a bag filter provided at the end of the dry exhaust gas treatment system. A method for recovering iron and phosphorus from steelmaking slag as described in 1.
(5) Any one of (1) to (4) above, wherein the slag recycling destination in the third step is an iron ore sintering step or a hot metal production step in a blast furnace. A method for recovering iron and phosphorus from steelmaking slag as described in 1.
(6) The above (1) to ((1), wherein the slag recycling destination in the third step is a hot metal preliminary dephosphorization treatment in a steelmaking refining step or a hot metal decarburization refining in a converter. The method for recovering iron and phosphorus from the steelmaking slag according to any one of 4).
(7) The reduction process of the first step and the reduction process of the second step are continuously performed in the same heating facility provided with a temperature difference. The method for recovering iron and phosphorus from steelmaking slag according to any one of (6) above.
(8) T. in the slag to be reduced in the second step. The method for recovering iron and phosphorus from steelmaking slag according to any one of (1) to (7) above, wherein the Fe concentration is adjusted to 5.0% by mass or less.

  According to the present invention, a steelmaking slag containing at least one of phosphorus out of preliminary dephosphorization slag generated during the preliminary dephosphorization treatment of hot metal and converter slag generated in the decarburization refining of hot metal in the converter. In recycling to a steelmaking process or a steelmaking process, first, the iron oxide contained in the steelmaking slag is recovered as reduced iron, and then the slag in which the iron oxide has been reduced is subjected to a reduction treatment to obtain phosphorous oxide in the slag. The steelmaking slag with reduced phosphorus content is recycled as a CaO source in the ironmaking process or the steelmaking process, while the recovered reduced iron is recycled as an iron source in the ironmaking process or the steelmaking process, Furthermore, the phosphorus removed to the gas phase side is recovered in a state where the phosphor oxide is concentrated to a level sufficient for recovery as a phosphoric acid resource raw material in the exhaust gas treatment system. Recycling of steel-containing slag containing phosphorus without any adverse effects such as increasing the concentration or impairing the function as a dephosphorizing agent has been realized, and at the same time, it is contained in steel-making slag. Effective utilization of iron and phosphorus as resources is realized.

In particular, in the recycling of steelmaking slag to the ironmaking process, the amount of blast furnace slag generated increases due to the iron ore sintering process or recycling to the blast furnace, but fine powdered blast furnace slag is used as an admixture for cement. As a result, the CaO content in the slag causes a pozzolanic reaction similar to that of the cement and develops the strength of the cement. Conventionally, the CaO content of the cement raw material has been manufactured by calcining calcium carbonate (CaCO ₃ ), and this calcining requires not only thermal energy but also generates CO ₂ gas. When mixed into a blast furnace slag cement (referred to as “blast furnace cement”), the firing energy and the amount of CO ₂ gas generated can be reduced according to the mixing ratio of blast furnace slag fine powder / ordinary Portland cement.

T. in the slag before the second reduction process. It is a figure which shows the relationship between Fe density | concentration and the unknown phosphorus rate after a reduction process.

  Hereinafter, the present invention will be described in detail.

The present inventors have made steelmaking slag containing phosphorus ("phosphorus-containing steelmaking slag" such as preliminary dephosphorization slag generated during preliminary dephosphorization of hot metal and converter slag generated during decarburization refining of hot metal in a converter. Is also used as a dephosphorization agent (= CaO for fixing P ₂ O ₅ ) or a CaO source as a fouling agent, when it is recycled in the ironmaking process or the steelmaking process, it contains phosphorus contained in the steelmaking slag. Is reduced in the reducing atmosphere of the blast furnace and shifts to hot metal, and the phosphorus concentration in the hot metal rises. First, the influence of phosphorus contained in this steelmaking slag on the hot metal discharged from the blast furnace is eliminated. Considered to do. That is, the method of removing phosphorus from phosphorus-containing steelmaking slag before recycling 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 understand. In this case, the phosphorus-containing steelmaking slag contains iron as an oxide in the form of FeO or Fe ₂ O ₃ (hereinafter collectively referred to as “Fe _x O”). Therefore, when phosphorus-containing steelmaking slag is reduced with a reducing agent such as carbon, silicon, or aluminum, Fe _x O in the steelmaking slag is also reduced.

  Phosphorus has high solubility in iron. Therefore, phosphorus produced by reduction dissolves rapidly in iron produced by reduction, and reduced iron having a high phosphorus concentration is produced. One of the objects of the present invention is to remove phosphorus from phosphorus-containing steelmaking slag to improve it into a steelmaking slag having a low phosphorus content. As another object, the produced reduced iron is used as an iron source. May be used effectively. When considering using reduced iron in the ironmaking process and steelmaking process, the lower the phosphorus concentration in the reduced iron, the less the dephosphorization load in the steelmaking process, so the phosphorus concentration in the reduced iron is low. It is desirable.

  Therefore, the present inventors have intensively studied and studied to reduce the phosphorus concentration in the reduced iron. In the study, when phosphorus is removed from the phosphorus-containing steelmaking slag and the modified low phosphorus slag is recycled to the iron making process, etc., in order to make the influence of phosphorus harmless, 70 mass of phosphorus in the phosphorus-containing steelmaking slag is used. It is desired to remove about 70% or more, and it is relatively easy to remove about 70% by mass of phosphorus contained in the phosphorus-containing steelmaking slag by reduction treatment. Then, the examination was started by setting the removal rate of phosphorus from the phosphorus-containing steelmaking slag by reduction treatment to 70%.

For example, T.W. Fe concentration (total value of iron content of all iron oxides in slag such as T.Fe: FeO and Fe ₂ O ₃ ) = 25 mass%, P concentration = 0.8 mass% 1 ton of steelmaking slag is reduced In this case, 250 kg of reduced iron is theoretically calculated. If the removal rate of phosphorus from the slag is 70%, the phosphorus produced by the reduction is 5.6 kg (= 1 ton × 0.8 mass% × 70%). When all of 5.6 kg of phosphorus is dissolved in reduced iron, the concentration of phosphorus in the reduced iron is approximately 2.2% by mass. Since the phosphorus concentration of a general blast furnace hot metal is about 0.1% by mass, the phosphorus concentration in the reduced iron is 20 times or more that of the blast furnace hot metal. When such reduced iron with a high phosphorus concentration is recycled as an iron source, naturally, the dephosphorization load in the steel making process increases, and the production cost increases.

However, as a result of the study, the reduction of the iron oxide in the phosphorus-containing steelmaking slag and the reduction of the phosphorus oxide were shifted, and the iron oxide in the slag was reduced first. It has been found that the phosphorus concentration of can be lowered. Further, by reducing the phosphorus oxide in the slag after the iron oxide is reduced and removed, the phosphorus-based gas generated in the reduction (in the form of P ₂ or P ₄ ) has iron in the vicinity thereof. In some cases, it easily dissolves in iron, but since no iron is present in the vicinity thereof, it has been found that the produced phosphorus-based gas is directly removed to the exhaust gas treatment system.

  In this way, iron oxide and phosphorus oxide in phosphorus-containing steelmaking slag are reduced stepwise, that is, iron oxide is mainly reduced first, and then phosphorus oxide is mainly reduced. When reduced iron having a low concentration is obtained and this reduced iron is recycled to the steelmaking process, excessive increase of the dephosphorization load in the steelmaking process is suppressed, and the slag after reducing and removing the phosphor oxide is reduced. Can be used as a CaO source in a steelmaking process or a steelmaking process. In other words, it has been found that stepwise reduction of iron oxide and phosphorus oxide in phosphorus-containing steelmaking slag has a great merit.

Therefore, the present inventors have verified experimentally operating conditions for reducing iron oxide in phosphorus-containing steelmaking slag in preference to phosphorus oxide and recovering reduced iron having a low phosphorus concentration. As a result, it was found that reduced iron having a low phosphorus concentration can be recovered by controlling the basicity of the slag and the reduction treatment temperature within an appropriate range. In the following, the transition of research that led to such conditions will be explained. In the present invention, the basicity of slag is defined by the ratio ((mass% CaO) / (mass% SiO ₂ )) between the CaO concentration and the SiO ₂ concentration in the slag.

When Fe _x O or P ₂ O ₅ in phosphorus-containing steelmaking slag is reduced with carbon, it is found that Fe _x O is more easily reduced than P ₂ O _{5 due} to the thermodynamic stability. ing. Based on this phenomenon, the present inventors considered that only the iron oxide can be reduced by setting the reduction treatment temperature relatively low. As a result of various reduction experiments, it was found that the iron oxide in the phosphorus-containing steelmaking slag is reduced when the reduction treatment temperature is 1100 ° C. or higher. When the reduction treatment temperature is less than 1100 ° C., more than half of the iron oxide in the slag remains as iron oxide without being reduced. It was also found that the upper limit of the reduction treatment temperature was 1300 ° C. When the reduction treatment temperature exceeds 1300 ° C., the iron oxide is sufficiently reduced, but the reduction of the phosphor oxide in the slag occurs, and the reduction rate of the phosphor oxide exceeds 30%. It also occurs when the phosphorus concentration of exceeds 1.0% by mass. When this reduced iron is recycled to the steelmaking process, the dephosphorization load increases.

Further, it has been found that in order to recover reduced iron, it is necessary to control not only the reduction treatment temperature but also the basicity of slag ((mass% CaO) / (mass% SiO ₂ )) within an optimal range. As a result of adjusting the reduction treatment temperature to a range of 1100 to 1300 ° C. and using phosphorus-containing steelmaking slag having different basicity, it was found that 1.0 to 3.0 is the optimal range for the basicity of slag. It was. When the basicity of phosphorus-containing steelmaking slag is less than 1.0, reduced iron can be recovered, but it is generated when the basicity is too low and the reduced slag is recycled to the ironmaking process or steelmaking process. In order to adjust the basicity of the slag, a CaO source is further required, resulting in an increase in the amount of blast furnace slag and steelmaking slag. On the other hand, when the basicity of the steelmaking slag exceeds 3.0, the iron oxide in the slag is reduced, but a part of the reduced iron remains as fine iron in the slag, and as reduced iron There is a demerit that it cannot be collected.

From the above results, in order to mainly reduce the iron oxide in the phosphorus-containing steelmaking slag and suppress the reduction rate of the phosphorus oxide in the phosphorus-containing steelmaking slag to 30% or less, the reduction treatment temperature is 1100 to 1300 ° C. And the basicity ((mass% CaO) / (mass% SiO ₂ )) of the whole reduction object including phosphorus-containing steelmaking slag needs to be in the range of 1.0 to 3.0. I found out.

Since the basicity of converter slag, which is representative of steelmaking slag, is usually about 3.0 to 5.0, when the present invention is applied, SiO containing SiO ₂ with respect to most converter slag. _It is necessary to mix the _two sources and adjust the basicity of the entire reduction target. Examples of the SiO ₂ source include silica, low basicity slag, and Si sludge generated in the manufacturing process of the solar cell. In particular, the preliminary dephosphorization slag generated during the preliminary dephosphorization treatment of the hot metal has a basicity of about 1.2 to 2.5, and the phosphorus concentration is lowered even if mixed because it is a slag containing phosphorus. Therefore, it is preferable to use preliminary dephosphorization slag as a basicity adjusting material for converter slag. Here, the preliminary dephosphorization slag is itself a phosphorus-containing steelmaking slag, but the converter slag functions as a SiO ₂ source.

In addition, "the whole reduction object" is added to the phosphorus-containing steelmaking slag in order to adjust the basicity to a range of 1.0 to 3.0 in addition to the phosphorus-containing steelmaking slag that is the original reduction object. The entire mixture including the SiO ₂ source to be mixed. When mixing the SiO ₂ source with the phosphorus-containing steel slag, it is preferable to mix it uniformly. Therefore, in this case, both the phosphorus-containing steel slag and the SiO ₂ source are crushed to a particle size of 10 mm or less and crushed. What is necessary is just to stir and mix each other with a mixer.

  Further, the present inventors reduce iron oxide, reduce slag after removing reduced iron produced by reduction of iron oxide by magnetic separation, etc., to reduce phosphorous oxide in slag again. The optimum conditions of the were verified. As a result, it was found that the optimum temperature for reducing and removing the phosphor oxide in the slag after reducing the iron oxide was in the range of 1350-1500 ° C. When this reduction temperature is lower than 1350 ° C., the phosphor oxide in the slag is not sufficiently reduced. On the other hand, when the reduction temperature exceeds 1500 ° C., the reduction rate of the phosphorous oxide in the slag is saturated and does not increase any more, and not only the energy consumption for heating increases but also the reduction. The demerit increases, for example, the damage to the refractories in the processing furnace increases.

Furthermore, the present inventors have studied and studied the recovery of phosphorus resources. By reducing the iron oxide and phosphorus oxide in the phosphorus-containing steelmaking slag in stages, there is no iron in the vicinity of the phosphorus-based gas generated by the reduction of the phosphorus oxide, and the phosphorus-based gas remains in the gas phase. Removed to the side. The phosphorus removed to the gas phase is sent to a dry exhaust gas treatment facility together with a gas mainly containing CO gas. In a dry exhaust gas treatment facility, CO gas becomes CO ₂ gas by secondary combustion treatment. At that time, phosphorus-based gases such as P ₂ gas and P ₄ gas are also oxidized, and finally, as the gas temperature lowers, It is inferred thermodynamically that it becomes a phosphorus oxide such as P ₂ O ₅ .

The inventors of the present invention installed a bag filter on the exit side of the dry exhaust gas treatment facility provided in the reduction experiment apparatus, and tried to capture phosphorous oxide using this bag filter. As a result, P ₂ O _5, which is a phosphor oxide, was confirmed from the bag filter together with slag physically scattered in the exhaust gas. The P ₂ O ₅ concentration of the fly ash captured by the bag filter was a high concentration exceeding 20% by mass. With such a high P ₂ O ₅ concentration, it is possible to find a value for recovery and use as a phosphoric acid resource raw material.

The present invention has been made based on these test results, and the method for recovering iron and phosphorus from the steelmaking slag according to the present invention is a preliminary method for slag and hot metal generated in the decarburization of hot metal in a converter. The basicity ((mass% CaO) / (mass% of the entire reduction object) of the steelmaking slag containing at least any one of the slag generated in the dephosphorization treatment is reduced including the steelmaking slag. % SiO ₂ )) is adjusted to be in the range of 1.0 to 3.0, and then reduced with a reducing agent containing carbon at a temperature of 1100 to 1300 ° C. to oxidize iron in the steelmaking slag. The first step of reducing the product to recover the reduced iron, and the slag whose amount of iron oxide has been reduced by the reduction treatment of the first step is reduced using a reducing agent containing carbon and contained in the slag Reduction removal to the gas phase The second step, the third step of recycling the slag having a reduced phosphorus content in the second step as a CaO source in the ironmaking step or the steelmaking step, and the reduced iron recovered in the first step A fourth step of recycling as an iron source in the iron making step or the steel making step, and phosphorus reduced and removed to the gas phase in the second step are recovered as phosphorous oxides in an exhaust gas treatment system and used as a phosphoric acid resource raw material. And 5 steps. Here, coke, coal, charcoal, char or the like is used as the reducing agent containing carbon.

  As a method for recycling steelmaking slag in which the content of iron oxide and phosphorous oxide has been reduced by the reduction treatment step, it is used as a CaO source (slagging agent) in the iron ore sintering step, and then hot metal in a blast furnace. In addition to the method used as the charging raw material in the manufacturing process, the method used directly as the CaO-based iron making agent in the hot metal manufacturing process in the blast furnace, or the CaO-based dephosphorizing agent in the preliminary dephosphorization treatment of the blast furnace hot metal Suitable methods include a method of using a slag or a method of using as a slagging agent in a decarburizing and refining process of hot metal in a converter, and a method of using as a CaO-based desulfurizing agent in a desulfurization treatment of blast furnace hot metal . Even if it is a process other than this, as long as it is the process which uses the quicklime (CaO) of the iron making process and steelmaking process in an ironworks, it can be used as a substitute for quicklime. Although the total amount of the converter slag generated may be subjected to the reduction treatment step of the present invention, it is effective from the viewpoint of resource saving to use the converter slag in the preliminary dephosphorization treatment of hot metal. It is preferable that a part of the generated converter slag is used as a CaO source (CaO-based dephosphorizing agent) in the hot metal preliminary dephosphorization process, and the remaining part of the converter slag is subjected to the reduction process of the present invention.

  Moreover, although said reduction | restoration process investigation experiment was performed with the rotary kiln type | mold processing container, what kind of thing may be used as a processing container as long as it can give a heat reduction to phosphorus containing steelmaking slag. In addition to the rotary kiln, for example, an arc heating type electric furnace, a converter having a heating device with a burner or oxygen, a pot-type processing container, an induction heating furnace, an RHF type processing container, and the like can be given.

  Moreover, although the said test performed separately the reduction process of the iron oxide in phosphorus containing steelmaking slag, and the reduction process of a phosphorous oxide using the rotary kiln type | mold processing container, using one rotary kiln type | mold processing container. In addition, a test in which the reduction treatment of iron oxide and the reduction treatment of phosphorous oxide were continuously performed was also performed. That is, in the rotary kiln having a plurality of burners, the first half region on the raw material charging side is 1100 to 1300 ° C., and the second half region is 1350 to 1500 ° C. to adjust the burner heating conditions to provide a temperature difference, Steelmaking slag whose basicity was adjusted to 1.0 to 3.0 was continuously charged into the rotary kiln to reduce steelmaking slag.

  As a result, the recovered amount of reduced iron, the concentration of phosphorus in the reduced iron, the concentration of phosphorus in the post-reduction slag, and the concentration of phosphorus in the recovered fly ash are similar to those in the test in which the reduction treatment was performed in two steps. I found out. On the other hand, the reduction treatment can be reduced from two times to one, and it has been confirmed that the operation cost can be reduced and the productivity can be improved by drastically reducing the amount of energy used, and the treatment cost can be greatly reduced. .

  That is, the object of the present invention can be achieved more efficiently by continuously performing the reduction treatment of iron oxide and the reduction treatment of phosphorous oxide in this order in the same heating equipment provided with a temperature difference. Was confirmed. In addition, as a means for providing a temperature difference in the same heating equipment, a means for arranging a plurality of burners in the furnace and providing a temperature difference by adjusting the output of each burner, a means for unevenly arranging heating elements, etc. Any other means may be used as long as it can be installed in the above-described equipment.

In addition, in the reduction process of the second step of reducing and removing phosphorous oxide to the gas phase, the inventors reduce the phosphorus-based gas such as P ₂ gas generated by the reduction of phosphorous oxide in the slag in the vicinity thereof. For the purpose of suppressing dissolution in iron (granular iron), T.I. in the slag to be reduced in the second step. We examined and studied the relationship between Fe concentration and phosphorus reduced and removed to the gas phase.

In the test, phosphorus-containing steelmaking slag whose basicity was adjusted to 1.0 to 3.0 was reduced at 1100 to 1300 ° C. under various reduction conditions (corresponding to the reduction treatment in the first step) and reduced. T. in slag after treatment Slags having an Fe concentration of about 3.0 to 10.0% by mass were produced, and then these slags were reduced again at 1350 to 1500 ° C. (corresponding to the reduction process in the second step). As a result, in the slag before the reduction treatment in the second step, T.A. It has been found that if the Fe concentration is 5.0% by mass or less, it is possible to suppress dissolution of phosphorus-based gas such as P ₂ gas in the reduced iron in the reduction process of the second step. That is, the T. slag in the slag to be reduced in the second step. It has been found that it is preferable to adjust the Fe concentration to 5.0% by mass or less in advance.

In the slag before the reduction treatment in the second step, T.P. As a method of adjusting the Fe concentration, in addition to the method of changing the reducing treatment conditions of the first step such as adjusting the amount of reducing agent used and the reducing time in the reducing treatment of the first step, One or more of a CaO source such as blast furnace slag and lime or a SiO ₂ source such as silica stone is added to the slag obtained by the reduction treatment, and T. slag in the slag is added. Examples include a method of diluting the Fe concentration, or a method of removing reduced iron by magnetically selecting the slag obtained by the reduction treatment in the first step shown below.

  The inventors of the present invention have confirmed that it is more effective to remove phosphorus in the gas phase after removing the metallic iron mixed in the slag to be subjected to the reduction treatment in advance. As described above, reduced phosphorus has high solubility in iron. Therefore, when iron is present in the vicinity of phosphorus, it immediately dissolves in iron and becomes phosphorus-containing iron. However, by removing metallic iron by pretreatment, the amount of iron produced by reduction can be reduced, so that the probability that phosphorus produced by reduction dissolves in reduced iron can be further reduced. For the prior metal iron separation, an appropriate process may be selected according to the shape and throughput of the slag, such as separation using magnetic force (magnetic separation) or centrifugal airflow separation using the specific gravity difference between iron and slag. .

  As described above, according to the present invention having the above-described configuration, at least one of preliminary dephosphorization slag generated during hot metal preliminary dephosphorization treatment and converter slag generated during decarburization refining of hot metal in a converter. In recycling a steelmaking slag containing one kind of phosphorus to a steelmaking process or a steelmaking process, first, iron oxide contained in the steelmaking slag is recovered as reduced iron, and then the slag with reduced iron oxide is recovered. Reduction treatment removes the phosphorous oxide in the slag to the gas phase, and the steelmaking slag having a reduced phosphorus content is recycled as a CaO source in the ironmaking process or the steelmaking process, while the recovered reduced iron is recovered in the ironmaking process or Phosphorus oxide, which is recycled as an iron source in the steelmaking process and further removed to the gas phase side, is concentrated to a level sufficient to be recovered as a phosphoric acid resource raw material in the exhaust gas treatment system. Therefore, it is possible to recycle the steelmaking slag containing phosphorus to the ironmaking process or the steelmaking process without increasing the phosphorus concentration of the hot metal or impairing the function as a dephosphorizing agent. At the same time, it is possible to effectively use iron and phosphorus contained in steelmaking slag as resources.

  In addition, the converter slag generated during the decarburization refining of the hot metal that has been subjected to the preliminary dephosphorization treatment up to the phosphorus concentration level of the steel product in advance also contains phosphorus instead of 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, there is a risk of increasing the cost. Therefore, the “steel-making slag containing phosphorus” targeted in the present invention means that when the steel-making slag is recycled to a blast furnace or the like, the hot metal or the phosphorous concentration of the molten steel increases, resulting in an increase in cost relative to normal operations. It is a steelmaking slag containing phosphorus at a concentration or higher.

  The blast furnace hot metal discharged from the blast furnace is received by a topped car, the blast furnace hot metal accommodated in the topped 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 hot metal is desulfurized by a mechanical stirring desulfurization device, the blast furnace hot metal after this desulfurization treatment is charged into the converter, and decarburization refining is performed in the converter, thus producing molten steel from the blast furnace hot metal. The present invention was applied in the steelmaking process. Table 1 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 1, the blast furnace hot metal after desiliconization and dephosphorization contains 0.050% by mass of phosphorus, which is higher than the phosphorus concentration level (0.015% by mass or less) of steel products. The converter slag generated by converter decarburization refining using this blast furnace hot metal contains about 0.8% by mass of phosphorus (about 1.8% by mass with P ₂ O ₅ ). When this converter slag is used as a CaO source in the iron ore sintering step, enrichment of phosphorus in the blast furnace hot metal occurs. Then, the test which applies this invention to this converter slag was implemented.

  200 tons of converter slag, silica as basicity adjusting material, and coke as reducing agent are charged into a rotary kiln equipped with a heating burner, and the converter slag, silica and coke are heated by the burner and converted. Reduction treatment of furnace slag was carried out. In the present invention, the iron oxide and the phosphorous oxide in the converter slag are reduced stepwise, the reduction of the iron oxide is referred to as the first stage reduction, and the reduction of the phosphorus oxide is referred to as the second stage reduction. After the first stage reduction, reduced iron and slag (mainly a mixture of converter slag with reduced iron oxide and silica and coke residue) are separated by magnetic separation, and recovered slag after the first stage reduction. Was charged again in the rotary kiln and the second stage reduction was carried out.

The amount of input coke was 16 tons in the first stage reduction and 4 tons in the second stage reduction. A test without gradual reduction was also carried out, and the amount of input coke at that time was 20 tons. In the second stage reduction, a dry exhaust gas treatment facility was provided on the exhaust gas outlet side of the rotary kiln, and a fly filter was collected by placing a bag filter at the end of the dry exhaust gas treatment facility. In the first stage reduction, the treatment temperature was adjusted and the basicity was adjusted by changing the amount of silica mixed, and in the second stage reduction, the treatment temperature was fixed at 1400 ° C. Table 2 shows test conditions and test results. The basicity after mixing shown in Table 2 is basicity ((mass% CaO) / (mass% SiO ₂ )) in a mixture of converter slag, silica and coke residue.

In Examples 1 to 9 of the present invention in which the basicity of the mixture in the first stage reduction is 1.0 to 3.0 and the reduction treatment temperature is 1100 to 1300 ° C., the reduced iron recovered in the first stage reduction is reduced. The mass was 42 to 49 tons, and the phosphorus concentration of this reduced iron was 0.19 to 0.48 mass%. In the inventive examples 1 to 9, the phosphorus concentration of the slag after completion of the second stage reduction is 0.13 to 0.19% by mass, the amount of fly ash recovered is 10 to 15 tons, The concentration of P ₂ O ₅ was as high as 21.0 to 31.2% by mass, and the recovered fly ash was sufficiently valuable as a phosphoric acid resource raw material. Furthermore, the phosphorus concentration of the reduced iron recovered in the second stage reduction was 0.38 to 0.98% by mass, which was slightly higher than the reduced iron in the first stage reduction, but the recovered amount was 3 to 10 tons. It was.

  On the other hand, in Comparative Example 1, as a result of not performing stepwise reduction treatment, the phosphorus concentration of the recovered reduced iron was as high as 1.78% by mass.

  In Comparative Examples 2 to 4, in the first stage reduction, the basicity of the mixture was 1.0 to 3.0 and within the range of the present invention, but the reduction treatment temperature was set to 1000 ° C. lower than the range of the present invention. It is. In Comparative Examples 2 to 4, the recovered amount of reduced iron in the first stage reduction was as low as 26 to 31 tons, and the iron oxide in the slag could not be sufficiently reduced and recovered. As a result, phosphorus was concentrated in the reduced iron recovered during the second stage reduction, and the phosphorus concentration in the reduced iron recovered during the second stage reduction was extremely high at 3.48 to 4.36% by mass. .

  In Comparative Examples 5 to 7, the basicity of the mixture in the first stage reduction was 1.0 to 3.0 and within the range of the present invention, but the reduction treatment temperature was set to 1400 ° C. higher than the range of the present invention. It is. In Comparative Examples 5 to 7, the recovered amount of reduced iron in the first stage reduction is as high as 48 to 51 tons, but the phosphorous oxide is also reduced because the reduction temperature is high, and the reduced phosphorus-based gas is reduced iron. The phosphorus concentration in the reduced iron was 1.06 to 1.56% by mass, which was higher than that of the examples of the present invention.

  Comparative Examples 8 to 10 are tests in which the basicity of the mixture was set to 3.5 higher than the range of the present invention in the first stage reduction, and the reduction treatment temperature was set to 1100 to 1300 ° C. within the range of the present invention. In Comparative Examples 8 to 10, the recovered amount of reduced iron in the first stage reduction was 21 to 35 tons. This is because the iron oxide in the slag could not be sufficiently reduced and recovered by the first stage reduction due to the high basicity of the mixture. Therefore, phosphorus is concentrated in the reduced iron recovered at the second stage reduction, and the phosphorus concentration in the reduced iron recovered at the second stage reduction is extremely high at 2.97 to 4.84% by mass. .

Further, P ₂ O ₅ concentration in the fly ash that is collected in Comparative Example 2-10 was below 15.0 wt% both.

  The slag after the second stage reduction in Invention Examples 1 to 9 was used as a CaO source for a flotation agent in the iron ore sintering step, and the manufactured sintered ore was charged into a blast furnace as an iron source. Hot metal was produced. The phosphorus concentration of the molten blast furnace iron was about 0.1% by mass, and almost no increase in phosphorus concentration was observed due to the recycling of steelmaking slag. In addition, although blast furnace slag cement was manufactured using blast furnace slag that was recycled after the second stage reduction, the quality was the same as before and there were no problems. Became possible.

  Moreover, although the slag after the 2nd stage | paragraph reduction | restoration in this invention examples 1-9 was used also as a CaO source for refining in a steelmaking process, refining operation could be performed without any problem. Moreover, although the reduced iron recovered in Invention Examples 1 to 9 was recycled to the iron making process and the steel making process, the phosphorus concentration was lower than that of the reduced iron of the comparative example, and no significant increase in dephosphorization load occurred. It was.

  Although not described in Table 2, as basicity adjusting material, Si sludge or low basicity slag of about 1 basicity generated in the steelworks was used instead of silica, but the reduction treatment was performed without any problem. Could be done. Further, not only the converter slag but also the preliminary dephosphorization slag was subjected to the reduction treatment, and it was possible to enjoy the effects of the present invention without any problem.

  For the inventive examples 1 to 9, when the converter slag generated in the steelmaking process is recycled as it is as a CaO source of sintered ore, the phosphorus concentration of the hot metal discharged from the blast furnace becomes high, and then The basic unit of CaO-based iron making agent and oxygen source in the steelmaking process increased, the amount of generated slag increased 1.5 times, and the productivity decreased by 20%.

  As the first stage reduction (reduction of iron oxide), 200 ton converter slag, 20 ton silica stone as basicity adjusting material, and 16 ton coke as reducing agent were equipped with a heating burner. The rotary kiln was charged, and the converter slag, silica and coke were heated by a burner to reduce the converter slag to 1300 ° C. and reduce the converter slag.

  The slag after the first stage reduction is recovered by magnetic separation, and 4 tons of coke is added to and mixed with the recovered slag, and this mixture is charged into a rotary kiln equipped with a heating burner to reduce the second stage (phosphoric acid). Reduction of the compound). The reduction treatment temperature at the second stage was changed in the range of 1300 to 1600 ° C., and the influence of the reduction treatment temperature on the second stage reduction was investigated. As in Example 1, fly ash was collected by the bag filter of the dry exhaust gas treatment facility in the second stage reduction.

Table 3 shows test conditions and test results. The basicity after mixing shown in Table 3 is basicity ((mass% CaO) / (mass% SiO ₂ )) in a mixture of converter slag, silica, and coke residue.

  In Example 10 of the present invention in which the treatment temperature of the second stage reduction was 1300 ° C., the phosphorus concentration in the slag after the second stage reduction was 0.33% by mass, and the treatment temperature of the second stage reduction was 1350 to 1600 ° C. It was slightly higher than Examples 11 to 16 of the present invention. On the other hand, in Inventive Examples 15 and 16, the reduction reaction in the second stage reduction was good, but it was recognized that the wear rate of the refractory in the furnace was slightly increased.

  From these results, it was confirmed that the reduction treatment temperature in the second stage reduction is preferably 1350 to 1500 ° C.

  As in Example 1, the slag after the second stage reduction was used as a CaO source for the iron making agent in the iron ore sintering step, and the produced sintered ore was charged into the blast furnace as the iron source. Manufactured. The phosphorus concentration of the molten blast furnace hot metal was about 0.1% by mass, and there was no problem. In addition, blast furnace slag fine powder and blast furnace slag cement were manufactured using blast furnace slag when the slag was recycled after the second stage reduction. The strength and other characteristics of JIS R 5211 “Blast Furnace Cement” are similar to the conventional ones, and there are no problems.

  In addition, as in Example 1, slag after reduction treatment is used in the steelmaking process, Si sludge or slag with low basicity is used as a substitute for silica stone, and preliminary dephosphorization slag is used for reduction treatment. There was no problem to serve.

  For the inventive examples 10 to 16, when the converter slag generated in the steelmaking process is recycled as it is as a CaO source of sintered ore, the phosphorous concentration of the hot metal discharged from the blast furnace becomes high, and then The basic unit of CaO-based iron making agent and oxygen source in the steelmaking process increased, the amount of generated slag increased 1.5 times, and the productivity decreased by 20%.

200 tons of converter slag, 7 to 60 tons of silica as a basicity adjusting material, and 20 tons of coke as a reducing agent are charged into a rotary kiln equipped with two heating burners before and after the rotary kiln. The temperature difference is set so that the first half of the raw material charging side is 1200 ° C and the second half is 1400 ° C, and the converter slag, silica and coke are heated by a burner to reduce the converter slag. (Invention Examples 17 to 19). A dry exhaust gas treatment facility was installed on the exhaust gas outlet side of the rotary kiln and a bag filter was placed at the end of the dry exhaust gas treatment facility to collect fly ash. Moreover, the reduction process of converter slag was implemented also in the rotary kiln set to 1400 degreeC for both the first half area | region and the latter half area | region for the comparison (comparative examples 11-13). Table 4 shows test conditions and test results. The basicity after mixing shown in Table 4 is basicity ((mass% CaO) / (mass% SiO ₂ )) in a mixture of converter slag, silica, and coke residue.

In Inventive Examples 17 to 19, the recovered reduced iron was 45 to 49 tons, and the phosphorus concentration was 0.31 to 0.49% by mass. Moreover, the phosphorus concentration of the slag after reduction was 0.18 to 0.21% by mass. The recovered fly ash was 7 to 9 tons, the P ₂ O ₅ concentration in the fly ash was as high as 20.0 to 29.8% by mass, and was sufficiently valuable as a phosphoric acid resource raw material.

  On the other hand, in Comparative Examples 11 to 13, as a result of not providing a temperature difference in the rotary kiln, the phosphorus concentration in the recovered reduced iron was as high as 1.67 to 1.91% by mass.

Here, the present invention 17, 18, and 19 are tests in which the reduction treatment under the conditions of the present invention examples 2, 5, and 8 in Example 1 was continuously performed in the same rotary kiln provided with a temperature difference. is there. As is clear from Tables 2 and 4, in the present invention examples 2, 5, 8 and the present invention 17, 18, 19, the recovery rate of reduced iron, the phosphorus concentration in the reduced iron, the slag in the reduced slag There is no significant difference between the phosphorus concentration and the P ₂ O ₅ concentration in the fly ash. Therefore, the present inventions 17, 18, and 19 can reduce the reduction treatment from two times to one time. , 5 and 8, not only can the operating cost such as energy intensity be greatly reduced, but also the productivity of the rotary kiln can be improved and the processing cost of the reduction treatment can be greatly reduced. .

  The temperature of the first half region on the raw material charging side of the rotary kiln is 1100 to 1300 ° C., the second half region is 1350 to 1500 ° C., and the basicity of the charged raw material after mixing is in the range of 1.0 to 3.0. In the tests, it was confirmed that reduction results comparable to those of the present invention 17, 18, 19 were obtained.

  For the inventive examples 17 to 19, when the converter slag generated in the steel making process is recycled as it is as a CaO source of sintered ore, the phosphorous concentration of the hot metal discharged from the blast furnace becomes high, and thereafter The basic unit of CaO-based iron making agent and oxygen source in the steelmaking process increased, the amount of generated slag increased 1.5 times, and the productivity decreased by 20%.

  As the first stage reduction (reduction of iron oxide), 200 ton converter slag, 20 ton silica stone as basicity adjusting material, and 16 ton coke as reducing agent were equipped with a heating burner. The rotary kiln was charged, and the converter slag, silica and coke were heated by a burner to reduce the converter slag to 1300 ° C. and reduce the converter slag. At this time, by adjusting the reduction treatment time, the T.O. A slag having an Fe concentration of about 3.0 to 10.0% by mass was produced.

  The slag after the first stage reduction is recovered by magnetic separation, and 4 tons of coke is added to and mixed with the recovered slag, and this mixture is charged into a rotary kiln equipped with a heating burner to reduce the second stage (phosphoric acid). Reduction of the compound). The reduction treatment temperature in the second stage was 1400 ° C.

Table 5 shows test conditions and test results. The basicity after mixing shown in Table 5 is basicity ((mass% CaO) / (mass% SiO ₂ )) in a mixture of converter slag, silica and coke residue.

  Here, the ratio of the phosphorus mass not contained in the slag and the reduced iron after the second stage reduction treatment to the phosphorus mass in the slag supplied as a raw material in the second stage reduction treatment is defined as the unknown phosphorus ratio (mass %). Therefore, “the unknown phosphorus ratio is high” means that there is much phosphorus reduced and removed to the gas phase.

  In Invention Examples 20 to 27, the T.V. in the slag before the second reduction treatment. FIG. 1 shows the relationship between the Fe concentration and the unknown phosphorus rate after the second reduction process. As apparent from FIG. 1, TC in the slag before the second reduction process. By making the Fe concentration 5.0% by mass or less, the unknown phosphorus rate is increased, the removal of phosphorus to the gas phase side is promoted, and the phosphorus-based gas to the granular iron existing in the vicinity of the phosphorus oxide is increased. It was confirmed that dissolution could be suppressed.

  When the slag basicity is in the range of 1.0 to 3.0, the first stage reduction treatment temperature is 1100 to 1300 ° C, and the second stage reduction treatment temperature is 1350 to 1500 ° C, Even in the case of T. It has been confirmed that the unknown phosphorus ratio increases under the condition that the Fe concentration is 5.0 mass% or less.

Claims (8)

Steelmaking slag containing at least any one of the slag generated in the decarburization and refining of hot metal in the converter and the slag generated in the preliminary dephosphorization treatment of hot metal is reduced including the steelmaking slag. After adjusting the basicity ((mass% CaO) / (mass% SiO ₂ )) of the entire reduction target to be in the range of 1.0 to 3.0, carbon is added at a temperature of 1100 to 1300 ° C. A first step of reducing the iron oxide in the steelmaking slag by recovering the reduced iron using a reducing agent contained;
A second step of reducing the slag whose amount of iron oxide has been reduced by the reduction treatment of the first step using a reducing agent containing carbon, and reducing and removing phosphorous oxide contained in the slag to the gas phase; ,
A third step of recycling the slag having a reduced phosphorus content by the second step as a CaO source in the iron making step or the steel making step;
A fourth step of recycling the reduced iron recovered in the first step as an iron source in the iron making step or the steel making step;
A fifth step of recovering and removing phosphorus reduced to the gas phase in the second step as a phosphorous oxide in the exhaust gas treatment system and using it as a phosphoric acid resource raw material;
A method for recovering iron and phosphorus from steelmaking slag, comprising: In the reduction treatment in the first step, the SiO ₂ source so that the basicity ((mass% CaO) / (mass% SiO ₂ )) of the whole reduction object is in the range of 1.0 to 3.0. The method for recovering iron and phosphorus from steelmaking slag according to claim 1, wherein:   The method for recovering iron and phosphorus from steelmaking slag according to claim 1 or 2, wherein in the second step, reduction treatment is performed at a temperature of 1350 to 1500 ° C.   The steelmaking slag according to any one of claims 1 to 3, wherein, in the fifth step, the phosphorus oxide is recovered using a bag filter provided at an end portion of the dry exhaust gas treatment system. For recovering iron and phosphorus from sewage.   The steelmaking slag according to any one of claims 1 to 4, wherein a recycling destination of the slag in the third step is an iron ore sintering step or a hot metal production step in a blast furnace. For recovering iron and phosphorus from sewage.   The slag recycling destination in the third step is either hot metal preliminary dephosphorization treatment in a steelmaking refining step or hot metal decarburization refining in a converter. A method for recovering iron and phosphorus from steelmaking slag according to item 1.   7. The reduction process of the first step and the reduction process of the second step are continuously performed in the same heating facility having a temperature difference. A method for recovering iron and phosphorus from steelmaking slag as set forth in any one of the above.   T. in the slag to be reduced in the second step. The method for recovering iron and phosphorus from steelmaking slag according to any one of claims 1 to 7, wherein the Fe concentration is adjusted to 5.0 mass% or less.

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