Title of the invention: Method for dechromizing molten pig iron and method for producing phosphoric acid fertilizer raw material
Technical field
[0001]
　The present invention particularly relates to a method for removing chromium from hot metal with suppressed dephosphorization during dechromation and a method for producing a phosphate fertilizer raw material.
Background technology
[0002]
　Since Japan has a large amount of rainfall, minerals are easily discharged from the soil and the soil is easily acidified. Therefore, as a phosphate fertilizer used when growing a plant, a basic phosphate fertilizer that increases not only the phosphate concentration in the soil but also the soil pH is widely used. At present, fused phosphorus fertilizer containing a large amount of alkali is used as a basic phosphate fertilizer.
[0003]
　On the other hand, in the integrated steelworks, the hot metal tapped from the blast furnace contains about 0.1% by mass of phosphorus as an impurity. Since phosphorus in steel is a harmful element that causes cold brittleness, phosphorus in hot metal is oxidized and removed by adding flux and blowing oxygen in the steelmaking process, and is discharged as steelmaking slag.
[0004]
　As shown in Patent Document 1, the concentration of phosphoric acid in steelmaking slag is about 1 to 4% by mass, which is not a sufficient concentration as a phosphate fertilizer, but in the steelmaking slag, CaO content derived from flux and oxidation from hot metal Since it contains a large amount of removed SiO 2, it is used as a silicate phosphate fertilizer.
[0005]
　However, even in Japan, where the total amount of phosphate rock, which is a raw material for phosphate fertilizers, is still dependent on imports, the phosphoric acid content in steelmaking slag is considered as a useful phosphate fertilizer resource. As shown in FIG. 4, it has been attempted to concentrate the phosphoric acid content in the steelmaking slag to produce a high-phosphoric acid slag and to produce a phosphate fertilizer from the steelmaking slag. Further, as disclosed in Patent Documents 5 to 7, techniques for enhancing the fertilizer effect by controlling the mineral phase in the slag are disclosed. Particularly in Patent Documents 6 and 7, high-P hot metal having a P concentration of 0.5 to 4.0 mass% is produced by reducing steelmaking slag containing phosphorus and iron, and the high-P hot metal is further dephosphorized. By doing so, a technique for producing high-phosphate slag and hot metal having a P concentration of about 0.1 mass% is disclosed.
[0006]
　On the other hand, if the fertilizer contains a large amount of heavy metals such as Cr, it may harm humans and animals that ate crops grown with the fertilizer, so the concentration of heavy metals in the fertilizer should be appropriate. Is required to be managed. For example, a part of the official standards for phosphate fertilizers specified in the Fertilizer Control Law stipulates that the Cr concentration be lowered.
[0007]
　As described above, many technologies for producing a phosphate fertilizer using steelmaking slag as a raw material have been disclosed. However, since the steelmaking slag sometimes contains heavy metals derived from scrap or stainless steel, especially Cr, when the steelmaking slag containing this Cr is subjected to reduction treatment in an electric furnace or the like, the Cr in the steelmaking slag is contained in the seed water. The concentration of Cr in the high P hot metal that is concentrated in the electric furnace and is tapped from the electric furnace may increase to 0.3 to 1.2 mass %. When the dephosphorization treatment is carried out as it is, a dechromization reaction also occurs at the same time as the dephosphorization, and the Cr concentration or chromic acid concentration in the high phosphoric acid slag becomes high, so that it cannot be sold as a fertilizer. Therefore, it is necessary to remove Cr in the hot metal in advance before performing the dephosphorization treatment of the high P hot metal. However, in order to improve the yield of the phosphate fertilizer during the dephosphorization treatment, it is required to suppress the dephosphorization reaction as much as possible when performing the dechromization treatment.
[0008]
　As a technique for removing Cr, Patent Document 8 discloses a technique for removing Cr from high P hot metal, and in this technique, basicity ( CaO mass%)/(SiO 2 mass%) is controlled to 0.1 or less, and an oxygen source is further added to carry out the dechromization treatment.
[0009]
　In recent years, in order to more efficiently produce a phosphate fertilizer raw material, it is desirable to use high P hot metal having a higher P concentration. The technique described in Patent Document 8 targets hot metal having a P concentration of 1.5 mass% as the hot metal subjected to dechromization treatment, and is difficult to apply when the P concentration in the hot metal is higher. The reason is as follows.
[0010]
　For example, when the dechromization treatment is performed on the hot metal having a high P concentration such as a P concentration of 3 mass %, the dephosphorization reaction is likely to proceed simultaneously with the dechromation reaction. As a result, the concentration of P 2 O 5 in the slag becomes higher than that of the hot metal having a low P concentration . Further, P 2 O 5 is an acidic oxide, has a low melting point, and has the property of lowering the liquidus temperature of slag. From this, as compared with the case where the hot metal having a low P concentration is subjected to the dechroming treatment, the production rate of Cr 2 O 3 during the dechromation reaction and the dechromation reaction are greatly affected.
Prior art documents
Patent literature
[0011]
Patent Document 1:
Japanese Patent No. 5105322 Patent Document 2: Japanese Patent Laid-Open No. 11-158526
Patent Document 3: Japanese Patent Laid-Open No. 2009-132544
Patent Document 4: Japanese Patent No. 5594183
Patent Document 5: Japanese Patent Laid-Open No. 2015-189591 Japanese
Patent Document 6: JP 2016-74940 JP
Patent Document 7: JP 2016-88757 JP
Patent Document 8: Japanese Patent No. 6119361
Summary of the invention
Problems to be Solved by the Invention
[0012]
　Therefore, in view of the above situation, the present invention provides a method for removing chromium from hot metal capable of suppressing the dephosphorization reaction and accelerating the dechromization reaction from high P hot metal produced using steelmaking slag as a raw material, and a phosphate fertilizer raw material satisfying fertilizer specifications. It is intended to provide a manufacturing method.
Means for solving the problem
[0013]
　In order to achieve the above-mentioned object, the present inventor conducted a study by focusing on the dechromization rate and the dephosphorization rate in terms of the flux and the manufacturing conditions used during the dechromization treatment of high P hot metal containing Cr. It has been found that the basicity dependency greatly differs between the dechromization rate and the dephosphorization rate, and by utilizing the difference, the dechromation reaction can be induced and the dephosphorization reaction can be suppressed.
[0014]
　The present invention based on the above findings is as follows.
(1)
　The basicity (CaO mass%)/(SiO 2 mass%) of slag is 0 with respect to the hot metal having a P concentration of 2 to 4 mass% and a Cr concentration of 0.3 to 1.2 mass%. .1 to less than 1 and deoxidized by supplying oxygen source in the hot metal temperature range of 1250 to 1500° C., P concentration is 1.9 to 3.8% by mass, and Cr concentration is Of less than 0.2% by mass is produced.
(2) The method for dechromizing hot metal according to (1) above, wherein the basicity of the slag is adjusted by adjusting the amount of flux added to 25 kg/t or less.
(3) The hot metal having a P concentration of 2 to 4 mass% and a Cr concentration of 0.3 to 1.2 mass% uses steelmaking slag obtained by dephosphorizing the hot metal produced in a blast furnace as a starting material. The method for removing chromium in hot metal according to the above (1) or (2), characterized in that
(4) A phosphate fertilizer raw material characterized in that the hot metal obtained by the method for dechromizing hot metal according to any one of (1) to (3) above is further subjected to dephosphorization treatment and cooling. Manufacturing method.
Effect of the invention
[0015]
　According to the present invention, there is provided a method for dechroming hot metal capable of suppressing dephosphorization reaction and accelerating dechromization reaction from high P hot metal produced using steelmaking slag as a raw material, and a method for producing a phosphate fertilizer raw material satisfying fertilizer specifications. be able to.
Brief description of the drawings
[0016]
FIG. 1 is a diagram showing an example of a step of producing phosphoric acid-containing slag in a steel making step.
FIG. 2 is a diagram showing the relationship between the basicity of slag and the dechromization rate and dephosphorization rate.
FIG. 3 is a diagram showing the relationship between the basicity of slag and the concentrations of chromic acid and phosphoric acid.
MODE FOR CARRYING OUT THE INVENTION
[0017]
　In the present invention, the basicity of slag (CaO mass%)/(SiO) with respect to high P hot metal having a P concentration of 2 to 4 mass% and a Cr concentration of 0.3 to 1.2 mass% in the hot metal. (2 % by mass) is more than 0.1 and 1 or less, and iron ore and/or gaseous oxygen is used as an oxygen source in the range of 1250 to 1500° C. to carry out the dechromization treatment. Then, after the Cr-containing slag generated at that time is discharged, the remaining hot metal is dephosphorized. The oxygen source is selected so that the hot metal temperature can be maintained appropriately.
[0018]
　The high P hot metal is characterized in that steelmaking slag produced by melting phosphorus in the hot metal produced in a blast furnace and then dephosphorizing is used as a starting material.
[0019]
　First, a method for producing phosphoric acid-containing slag that can be used as a raw material for a phosphate fertilizer for plant growth (phosphoric acid fertilizer raw material) using steelmaking slag as a raw material will be described. FIG. 1 shows an example of a process for producing phosphoric acid-containing slag in the steelmaking process.
[0020]
　As shown in FIG. 1, in the steelmaking process, the hot metal produced in a blast furnace, which normally contains 0.08 to 0.15% by mass of phosphorus, is transferred to a converter to form slag on the hot metal. After forming and blowing an oxygen source, the hot metal and slag are reacted to perform a dephosphorization treatment S01 of the hot metal.
[0021]
　The converter dephosphorization slag 41 generated by the dephosphorization treatment S01 is discharged from the converter, and then the slag is formed again on the hot metal in the converter, and the oxygen source is blown in to perform the decarburization treatment S02. The molten steel obtained in the decarburization treatment S02 is subjected to secondary refining S03, and then a steel slab is manufactured by continuous casting S04.
[0022]
　After the dephosphorization process S01, the converter dephosphorization slag 41 discharged from the converter contains a large amount of iron together with phosphoric acid obtained by oxidizing phosphorus in the hot metal. Therefore, in order to recover valuable elements such as iron and phosphorus from the converter dephosphorization slag 41, the converter dephosphorization slag 41 is subjected to a reduction/reformation treatment S11.
[0023]
　In the reduction/reformation treatment S11, the converter dephosphorization slag 41 is melted, and pulverized coal, Al 2 O 3 source, and SiO 2 source are added as a reducing agent and a modifier , and Cr is added in an amount of 0.3 to 1 The high P hot metal 42 containing a large amount of 0.2 mass% and P of 2 to 4 mass% is manufactured.
[0024]
　Then, the high-P hot metal 42 is received in a pan, and a flux containing a CaO source such as quicklime and calcium carbonate and a SiO 2 source such as silica sand is added to the pan to make the basicity of the slag more than 0.1 to 1 or less. The concentration of Cr is less than 0.2% by mass and the concentration of P is 1.9 to 3 by adding iron ore and/or blowing gaseous oxygen as an oxygen source at a hot metal temperature of 1250 to 1500° C. A low Cr, high P hot metal 43 of 0.8 mass% is produced. If the Cr concentration is less than 0.2% by mass, then, when the phosphoric acid fertilizer raw material described in, for example, Patent Document 5 or 6 is produced from the low Cr high P hot metal 43, the fertilizer within the standards in the Fertilizer Control Law Can be manufactured.
[0025]
　When the hot P hot metal 42 is received in the pan, the slag remaining in the reduction furnace (basicity : 0.9 to 1.3, Al 2 O 3 : about 10% by mass, t.Fe<5 About 10 kg/t of (mass %) is also carried over as slag, which is inevitably discharged into the pan together with the hot metal. In order to suppress the dephosphorization reaction as much as possible and accelerate the dechromization reaction, it is necessary to add a flux to adjust the basicity. Here, if the amount of slag is too large, the slag may overflow from the pot, and particularly in the case of the pot, it is difficult to stir, and thus the slag/metal reaction may not be sufficiently performed. In operation, the amount of slag in the pan is preferably 50 kg/t or less, so the amount of flux to be added is preferably 25 kg/t or less, considering the amount of generated chromic acid and phosphoric acid, and about 20 kg/t. It often becomes. In addition, when the carry-over slag has a basicity of 1.0 or less and the Cr concentration of the high P hot metal tapped from the reduction furnace is low, the de-chroming reaction is performed only with the carry-over slag and the Cr concentration is 0. It is possible to produce a low Cr, high P hot metal having a P content of less than 0.2 mass% and a P concentration of 1.9 to 3.8 mass %. Therefore, in such a case, the addition of flux is unnecessary.
[0026]
　For the low-Cr, high-P hot metal 43, a flux is added after the Cr-containing slag is discharged and a dephosphorization process S13 is performed to manufacture the phosphoric acid-containing slag 50. At this time, for the dephosphorization treatment S13, the technique described in Patent Document 6 or 7 is used. That is, in the dephosphorization treatment, the basicity is 0.8 to 1.5 and the iron oxide concentration is t. A flux containing 10% by mass or more in Fe concentration is added and oxygen is blown into the molten metal so that the hot metal temperature at the end of the treatment is in the range of 1200°C to 1450°C. In addition, after the phosphoric acid concentration in the slag becomes 5% by mass or more in the course of the dephosphorization treatment, a secondary material is further added to make the basicity α of the final slag 1.5 or more and 3.0 or more. The concentration of phosphoric acid in the slag is adjusted to 8 to (-4α 2 +23α-4)% by mass, and the concentration of iron oxide (calculated as Fe) is adjusted to 5 to 25% by mass. Thus, the phosphoric acid-containing slag 50 is manufactured.
[0027]
　Then, in the cooling process S14, the temperature drop amount from 1200 to 1450° C. which is the temperature at the end of the dephosphorization process to 600° C. is divided by the time until the temperature reaches 600° C. The cooling rate is 10° C./min or more. In addition, the pulverization process S15 is also performed as necessary to obtain the phosphate fertilizer raw material 60. The obtained phosphate fertilizer raw material 60 contains CaO, SiO 2 , P 2 O 5 , and iron oxide (converted to Fe) in a total amount of 60 mass% or more, and has a basicity α of 1.5 or more and 3.0 or less. A phosphoric acid fertilizer raw material containing P 2 O 5 in an amount of 8% by mass or more and (-4α 2 +23α-4)% by mass or less and iron oxide in an amount of 5% by mass or more and 25% by mass or less in terms of Fe. Among fertilizer raw materials, Ca 3 (PO 4 ) 2 —Ca 2 SiO 4 solid solution, 5CaO·SiO 2 ·P 2 O 5 and 7CaO·2SiO 2 ·P The total concentration of one or more of 2 O 5 present is 28% by mass or more.
[0028]
　The hot metal 51 dephosphorized to a phosphorus content concentration of 0.1 to 0.3 mass% by the dephosphorization treatment S13 is supplied to the converter together with the hot metal produced in the blast furnace.
[0029]
　Hereinafter, in the dechromization treatment, in order to accelerate the dechromization reaction of high-P hot metal containing Cr in an amount of 0.3 to 1.2 mass% and suppress the dephosphorization reaction, (1) the reason for limiting the hot metal component composition, (2) The reason for limiting the basicity in the slag and (3) the reason for limiting the treatment temperature will be described.
[0030]
(1) Composition of high P hot metal The dechromization
　treatment is affected by the composition of high P hot metal during the dechromization treatment. In the present invention, high-P hot metal having a Cr concentration in the hot metal of 0.3 to 1.2% by mass and a P concentration of 2 to 4% by mass is targeted. 3 to 1.2% by mass, C concentration 3.0 to 5.0% by mass, Si concentration 0.6% by mass or less, Mn concentration 0.3 to 1.4% by mass, P concentration 2.5. ~4.0% by mass of hot metal.
[0031]
(2) Basicity in Slag
　Next, the basicity (CaO mass%)/(SiO 2 mass%) in the slag needs to be more than 0.1 and 1 or less. If the basicity is 0.1 or less, the melting point of the slag increases due to a small amount of CaO, and it becomes difficult to discharge the Cr-containing slag after that, so the basicity is set to more than 0.1. The basicity is preferably 1.5 or more, more preferably 0.3 or more. Further, the upper limit of basicity was specified by the following experiment.
[0032]
　Using a 1t melting furnace, an experiment of dechromization treatment of high P hot metal having a Cr concentration of 0.3 to 1.2 mass% and a P concentration of 3 mass% was carried out. In the experiment, flux was added so that the amount of slag was about 50 kg/t and the basicity was in the range of 0 to 2, the treatment temperature was set to 1400° C., and iron oxide and oxygen were added in a total amount of 21 kg/t. .. The Cr concentration in the hot metal after the experiment was 0.1 to 0.2 mass %.
[0033]
　Fig. 2 shows the results of calculating the dechromization rate and the dephosphorization rate from the Cr concentration and P concentration in the hot metal before and after the experiment, and in Fig. 3, the chromic acid and phosphoric acid concentrations in the slag after the dechromization treatment are shown. Indicates. The dechromization rate and the dephosphorization rate also increased with the increase of basicity, but the dephosphorization rate was more influenced by the basicity and the phosphoric acid concentration in the slag showed a large difference. In order to increase the phosphorus recovery rate in the dephosphorization treatment after the dechromization treatment, it is necessary to suppress the dephosphorization rate in the dechromization treatment. From the results shown in FIG. 2, when the basicity exceeds 1, the dependency of the dephosphorization rate on the basicity becomes strong. Therefore, the basicity must be 1 or less in order to suppress the dephosphorization reaction while causing the dechromation reaction. The basicity is preferably 0.9 or less, and more preferably 0.85 or less.
[0034]
(3) Treatment temperature
　When producing low Cr, high P hot metal, it is necessary to adjust the above composition and basicity and further to perform hot metal treatment at a temperature of 1250 to 1500°C. Since the temperature of the molten slag is considered to be almost equal to the hot metal temperature, if the hot metal temperature is less than 1250°C, the slag may not be completely melted. Fertilizer effect does not appear. On the other hand, since the dechromation reaction is an exothermic reaction, the higher the temperature, the less likely the reaction proceeds. Therefore, when the temperature of the hot metal exceeds 1500° C., the concentration of chromic acid in the slag decreases. In addition, the heating cost is high and the refractory material in the processing container is heavily worn. The hot metal temperature is preferably 1300 to 1450°C.
[0035]
　Although the technique for performing the dechromization treatment from the high P hot metal has been described above, the present invention is not limited to the above description, and can be appropriately modified without departing from the technical idea of ​​the invention.
Example
[0036]
　Next, an example of the present invention will be described. The condition in the example is one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is based on this one condition example. It is not limited. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
[0037]
　First, high P hot metal having the initial hot metal composition shown in Table 1 below was discharged into a pan together with the carry-over slag, and dechromization treatment was performed at the temperature, the amount of flux added, and the amount of oxygen shown in Table 1. The composition in the hot metal was examined before and after the dechromization treatment, and the composition of the Cr-containing slag after the dechromization treatment was also investigated.
[0038]
　First, the slag slag was evaluated as follows: slag that was able to be slag was evaluated as ○, slag that was capable of being slag waste that took a little time to be discharged, and slag that was difficult to dispose was evaluated as x. Next, as a comprehensive evaluation, under the conditions where the dephosphorization rate is 15% or less and the dechromation rate is 70% or more, those having no problem in the slag are ◎, and the dephosphorization rate is 15% or less and the dechromization rate is The rate was 70% or more, but it took a little time for the slag to be removed, and the dephosphorization rate was greater than 15%, the slag was difficult to remove, or the dechromization rate was less than 70%. Was evaluated. The dechromization rate and the dephosphorization rate were calculated from the initial hot metal composition and the hot metal composition after the dechromization treatment.
[0039]
[table 1]

[0040]
　In Examples 1 to 8, the basicity of the slag was less than 0.1 and 1 or less with respect to the hot metal having a P concentration of 2 to 4 mass% and a Cr concentration of 0.3 to 1.2 mass% in the hot metal. As an oxygen source, iron ore and gaseous oxygen were used in the range of 1250 to 1500°C. As a result, in Examples 1 to 8, the slag containing Cr could be discharged without any problem, and the dephosphorization rate was 15% or less and the dechromation rate was 70% or more.
[0041]
　Comparative Example 1 is an example in which the basicity was more than 1, and shows the result when the dechromization treatment was performed under the conditions within the above range except the basicity. Since the basicity was over 1, the dephosphorization reaction also proceeded and the dephosphorization rate became 30%. Comparative Example 2 is an example in which the basicity was 0.1 or less as a result of not adding CaO, and shows the result when the dechromization treatment was performed under the conditions within the above range except the basicity. ing. In this case, the basicity was too low and the melting point of the slag was high, so that the Cr-free slag could not be efficiently discharged. Comparative Example 3 shows the results when the treatment temperature was 1,540° C. and the dechromization treatment was performed under the conditions other than the treatment temperature within the above range. Since the treatment temperature was high, the dechromation reaction was difficult to proceed, and the dechromation rate was 60% or less. Comparative Example 4 was an example in which the P concentration was less than 2.0 in the initial hot metal composition, so the dephosphorization rate was very low, but the dechromation rate was also low. It is considered that this is because the P concentration was too low in the initial hot metal composition, so that the basic range was not optimal when the basicity was more than 0.1 and 1.0 or less.
Industrial availability
[0042]
　According to the present invention, there is provided a method for dechroming hot metal capable of suppressing dephosphorization reaction and accelerating dechromization reaction from high P hot metal produced using steelmaking slag as a raw material, and a method for producing a phosphate fertilizer raw material satisfying fertilizer specifications. be able to.
The scope of the claims
[Claim 1]

　The basicity (CaO mass %)/(SiO 2 mass %) of slag is more than 0.1 with 　respect to the hot metal having a P concentration of 2 to 4 mass% and a Cr concentration of 0.3 to 1.2 mass %. The content of P is 1.9 to 3.8% by mass, and the Cr concentration is 0.1% by adjusting the temperature to 1 or less, and supplying the oxygen source in the hot metal temperature range of 1250 to 1500°C. A method for removing chromium from hot metal, which comprises producing less than 2% by mass of hot metal.
[Claim 2]
　The method for removing chromium from hot metal according to claim 1, wherein the basicity of the slag is adjusted by adjusting the amount of flux added to 25 kg/t or less.
[Claim 3]
　The hot metal having a P concentration of 2 to 4% by mass and a Cr concentration of 0.3 to 1.2% by mass is obtained by dephosphorizing the hot metal produced in a blast furnace and using the steelmaking slag as a starting material. The method for removing chromium from hot metal according to claim 1 or 2, which is characterized in that.
[Claim 4]
　A method for producing a phosphate fertilizer raw material, characterized in that the hot metal obtained by the method for dechromizing hot metal according to any one of claims 1 to 3 is further subjected to dephosphorization treatment and cooling.