JP7040499B2 - Phosphorus removal method from phosphorus-containing substances and steel manufacturing method - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention aims to improve the quality of a final metal product by reducing phosphorus in a phosphorus-containing substance used as a main raw material or an auxiliary raw material in advance in a metal smelting stage or a metal refining stage. The present invention relates to an effective method for removing phosphorus from a phosphorus-containing substance, and the present invention relates to a method for producing steel using a phosphorus-containing substance in which phosphorus has been reduced in advance as a main raw material or an auxiliary raw material.

[Definition]
In the present specification, when it is written in alphabets such as "P" and "P ₂ O ₅ ", it means a substance having the chemical formula, and when it is written in katakana as "phosphorus", it means phosphorus contained in the substance regardless of its form. Represents.

Further, when the volume of gas is expressed in the unit of "liter" in this specification, it is converted into a standard state where the temperature is 273 K and the atmospheric pressure is 1 atm. The unit of pressure atm is 1.01325 × ¹⁰⁵ Pa. When the P content in the substance is expressed in mass%, the phosphorus content in the substance is shown regardless of the form.

The hot metal melted in a blast furnace usually contains phosphorus (P) derived from an iron-making raw material component (solid oxide) such as iron ore inevitably. Since the phosphorus is considered to be a harmful component for steel products, in order to improve the material properties of steel products, it is usual to reduce the phosphorus by dephosphorus treatment mainly in the ironmaking and steelmaking processes. For example, as the dephosphorization treatment, phosphorus in hot metal or molten steel is oxidized with an oxygen source such as oxygen gas or iron oxide to obtain P ₂ O ₅ , and then this P ₂ O ₅ is mainly composed of CaO. There is a method of removing it by migrating it into the slag. In addition, phosphorus in hot metal or molten steel is oxidized by a gas such as oxygen and removed in slag, but iron is also oxidized at that time, so even if iron oxide is not used as an oxygen source. Even if there is, iron is also contained in the slag in the form of iron oxide.

In recent years, from the viewpoint of environmental measures and resource saving, there have been attempts to reduce the amount of steelmaking slag generated, including the recycling of steelmaking slag. For example, slag generated during decarburization and refining of hot metal that has been subjected to preliminary dephosphorization treatment (a treatment that removes phosphorus in the hot metal in advance before decarburizing and refining the hot metal in a converter) (hereinafter referred to as "converter slag"). This is because, in addition to being able to be used as a CaO source or iron source for slag-making agents, there are attempts to recycle it into a blast furnace by using it as a sintering raw material, or as a CaO source in a hot metal pretreatment step.

Pre-dephosphorized hot metal (hereinafter referred to as "de-phosphorus hot metal"), especially dephosphorized hot metal that has been pre-dephosphorized to the phosphorus concentration level of steel products, is at this time when it is decarburized and refined in a converter. The generated converter slag contains almost no phosphorus. Therefore, for example, even if such converter slag is recycled to a blast furnace, there is no need to worry about an increase in the phosphorus concentration (pickup) of the hot metal. However, slag generated during the pre-phosphorus removal treatment, hot metal that has not been pre-dephosphorused (hereinafter referred to as "normal hot metal"), or even if the pre-phosphorus treatment has been performed, the phosphorus concentration after the pre-phosphorus treatment is the phosphorus concentration of steel products. In the case of converter slag (slag containing a large amount of phosphorus) generated when decarburized and refined dephosphorized hot metal that has not decreased to the concentration level, it is recycled into a blast furnace in the form of oxide. Then, the phosphorus is reduced in the blast furnace, the phosphorus content in the molten metal increases, and the load of hot metal dephosphorus increases.

Further, in order to improve the strength of the steel product, it is effective to add manganese (Mn). Therefore, when manganese-containing steel is melted, manganese ore, ferromanganese with a carbon content of 1.0 to 7.5 mass% or less, and a carbon content of 2.0 mass are used to increase the Mn concentration in the molten steel. A manganese source such as silicon manganese having a carbon content of 0.01 mass% or less and metallic manganese having a carbon content of 0.01 mass% or less is used. However, it is known that the raw material prices of other manganese sources other than manganese ore increase as the carbon content decreases. Therefore, for the purpose of reducing the manufacturing cost, manganese-containing steel is smelted using inexpensive manganese ore as a manganese source. However, cheap manganese ore contains a large amount of phosphorus, and if it is used as a manganese source, there is a problem that the phosphorus concentration in the steel material increases and the quality deteriorates, and the use of manganese ore is restricted. The reality is that it is.

As described above, a large amount of phosphorus is generally contained in the main raw material or the auxiliary raw material used in the steelmaking process, and finally obtained depending on the phosphorus concentration contained in the phosphorus-containing substance and the amount used thereof. The phosphorus content in steel products increases. Since the phosphorus content adversely affects the quality of the steel product, it is required to suppress the phosphorus content in the steel product, and for that purpose, the use of a main raw material or an auxiliary raw material having a low phosphorus content is used. Is required. However, this will increase costs. Therefore, conventionally, some techniques for removing phosphorus in advance from a phosphorus-containing substance composed of a main raw material or an auxiliary raw material for steelmaking have been proposed.

For example, in Patent Document 1, iron ore having a CaO content of 25 mass% or less and a CaO / (SiO ₂ + Al ₂ O ₃ ) ratio of 5 or less, titanium-containing iron ore, nickel-containing ore, chromium-containing ore, or these ores. We propose a method for removing phosphorus by contacting a mixture containing the above-mentioned main component with Ar, He, N _2, CO, H _2, a kind of hydrocarbon or a mixed gas thereof at 1600 ° C. or higher.

Further, in Patent Document 2, iron ore having a high phosphorus content is crushed to 0.5 mm or less, water is added thereto to make the pulp concentration around 35 mass%, and H ₂ SO ₄ or HCl is added to the solvent to pH 2. Phosphorus minerals are decomposed and eluted by reacting at 0.0 or less, and then magnetite and other magnetic deposits are collected by magnetic force sorting to settle and separate non-magnetic deposits such as SiO ₂ and Al ₂ O ₃ as slime. A method has been developed in which P eluted in the liquid is neutralized in the range of pH 5.0 to 10.0 by adding slaked lime or quick lime, and separated and recovered as calcium phosphate.

Further, Patent Document 3 has developed a method for dephosphorizing iron ore by using the microorganism Aspergillus SP KSC-1004 strain or the microorganism Fusarium SP KSC-1005 strain.

Further, Non-Patent Document 1 reports on the reduction of high-phosphorus iron ore by a hydrogen-steam mixed gas in which the water vapor pressure is controlled, and proposes a method of directly dephosphorizing from iron ore.

Japanese Unexamined Patent Publication No. 54-8363 Japanese Unexamined Patent Publication No. 60-261501 Japanese Unexamined Patent Publication No. 2000-119759

Iron and Steel Vol. 100 (2014), No. 2, p. 325

However, each of the above-mentioned conventional techniques has the following problems to be solved.
That is, the method disclosed in Patent Document 1 has a problem that the processing temperature is as high as 1600 ° C. or higher and a large amount of energy is required. Further, since this method treats the ore in a molten state, there are problems that the container is worn and it is difficult to handle the high temperature melt.

Next, the method disclosed in Patent Document 2 is a wet treatment using an acid, and has a problem that it takes time and cost to dry the recovered magnetic substance as a main raw material. Further, this method has a problem that it takes time and cost to pulverize to 0.5 mm or less in advance.

Further, since the method disclosed in Patent Document 3 is wet-treated in the same manner as the method disclosed in Patent Document 2, there is a problem that it takes time and cost to dry the ore after removing phosphorus as a main raw material. ..

Further, Non-Patent Document 1 has a problem that the phosphorus removal rate in the ore is as low as 13% at the maximum. Moreover, since this method uses hydrogen as a reaction gas, it is necessary to study equipment for safe treatment on an industrial scale, but there is also a problem that it has not been done.

Therefore, the present invention is a method developed to solve the above-mentioned problems of the prior art, and an object thereof is a solid used as a main raw material or an auxiliary raw material for metal smelting or metal refining. It is to propose a method for removing phosphorus from a phosphorus-containing substance, which can be applied on an industrial scale, in order to effectively reduce phosphorus in a phosphorus-containing substance which is an oxide. Further, it is proposed a method for producing low phosphorus steel which can achieve both reduction of iron loss by reducing the amount of refining agent used and reducing the amount of slag generated by using the raw material from which phosphorus has been removed in this way.

In examining the above-mentioned problems of the prior art, the inventors efficiently remove phosphorus by heating the phosphorus-containing substance under a reduced pressure of less than atmospheric pressure and bringing it into contact with a gas containing nitrogen. I figured out what would happen.

The present invention is a method developed based on such findings. That is, the present invention is first a method of reacting a phosphorus-containing substance used as a raw material for metal smelting or metal refining with a nitrogen-containing gas to remove phosphorus in the phosphorus-containing substance by nitriding. Phosphorus mononitride is obtained by reducing the total pressure PA (Pa) of the atmosphere to less than atmospheric pressure, heating the phosphorus _- containing substance to a treatment temperature T (° C.) in an unmelted state, and reacting with the nitrogen-containing gas. We propose a method for removing phosphorus from a phosphorus-containing substance, which comprises producing (PN) and removing at least a part of phosphorus from the phosphorus-containing substance.

In addition, the method for removing phosphorus from the phosphorus-containing substance according to the present invention configured as described above is also described.
a. The nitrogen-containing gas has an adjusted nitrogen fraction _NN2 and oxygen partial pressure _PO2 (Pa).
b. The nitrogen-containing gas contains a reducing gas, and the nitrogen fraction _NN2 is adjusted so as to satisfy the condition of the following formula 1.
c. The treatment temperature T (° C.) satisfies the condition of the following formula 2 (in the formula, T _m represents the melting temperature (° C.) of the phosphorus-containing substance), and the oxygen partial pressure _PO2 (Pa) in the nitrogen-containing gas is satisfied. ) Meets the condition of formula 3 below.
It is considered that such as can be a more preferable embodiment.
Here, the nitrogen fraction _NN2 is {nitrogen concentration (vоl%) / 100}.

In the present invention, the term “under reduced pressure below atmospheric pressure” refers to a state in which the atmospheric pressure inside the reaction vessel is lowered from the atmospheric pressure outside the reaction vessel by a decompression device such as a vacuum pump. Further, the melting temperature _Tm is a temperature at which the solid sample changes to a liquid, and it is simple and desirable to determine by any of the following first to third methods, but the melting temperature is limited to these methods. It's not something to do.
-In the first method, a solid sample is placed in a container such as a melting point, and the temperature is raised to 5 ° C. per minute, preferably 1 ° C. or less per minute by an electric resistance furnace or the like under the target gas atmosphere. This is a method in which the melting point is the temperature at which the gaps between the grains of the solid sample disappear and a smooth surface is formed on the surface by continuously observing the sample inside.
-The second method measures the temperature of the minimum endothermic peak when the temperature is raised to 5 ° C. per minute, preferably 1 ° C. or less per minute by a differential thermal analysis method under the target gas atmosphere. It is a method of setting the melting point. Here, when a plurality of heat absorption peaks occur, the measurement is stopped at the temperature at which each heat absorption peak occurs, the appearance of the measurement sample is observed, the gaps between the grains of the solid sample disappear, and a smooth surface is generated on the surface. This is a method in which the temperature at the minimum point of the heat absorption peak, which is the lowest temperature among the temperatures, is used as the melting point.
-The third method is to use the thermodynamic calculation software of a computer to input the sample composition and change the temperature to calculate the liquid phase ratio, and set the temperature at which the calculated liquid phase ratio exceeds 95% as the melting point. Is.

The present invention is secondly a method for producing steel, which is contained by the method for removing phosphorus from the phosphorus-containing substance in at least one of the metal smelting step and the metal refining step. We propose a method for producing steel, which comprises using iron ore or manganese ore from which a part of phosphorus has been removed as at least a part of a raw material to produce steel.

According to the present invention, a solid such as a phosphorus-containing main raw material or auxiliary raw material, which is a raw material for metal smelting or metal refining, that is, a phosphorus-containing substance, is exposed to a temperature in an unmelted state under a reduced pressure of less than atmospheric pressure. By heating to and in contact with a nitrogen-containing gas, it becomes possible to efficiently perform smelting and dephosphorization of phosphorus in the phosphorus-containing substance with nitrogen. The amount used can be increased, and the load on the dephosphorization process in the metal smelting or metal refining process can be reduced.

Further, according to the present invention, by removing phosphorus from by-products such as steelmaking slag, the possibility of reuse of the by-products in the development process is expanded, and the amount of auxiliary materials used in the steelmaking process is reduced and secondary substances are used. It is possible to control the amount of biological generation.

Further, according to the present invention, phosphorus _denitrated is oxidized in exhaust gas to P2O5, and dust having a _high phosphorus concentration can be recovered, so that it can be effectively used as a phosphorus resource. There is also a side effect of becoming.

Regarding the reaction (a) for removing phosphorus as a gas of PN and the equilibrium reaction (c) between solid carbon and carbon monoxide gas, the treatment temperature T (° C.) and the oxygen partial pressure (logP) when the equilibrium of each reaction is established. It is a graph which shows the relationship of _O2 ). Graph showing the influence of the treatment temperature T (° C.) and the oxygen partial pressure _PO2 (Pa) on the phosphorus removal rate (ΔP) of iron ore at the total pressure _PA = 9.0 × 10 ⁴ Pa shown in Table 3-1. Is. Graph showing the influence of the treatment temperature T (° C.) and the oxygen partial pressure _PO2 (Pa) at the total pressure _PA = 1.0 × 10 ³ Pa shown in Table 3-2 on the phosphorus removal rate (ΔP) of iron ore. Is. FIG. 3 is a graph showing the effects of the treatment temperature T (° C.) and the oxygen partial pressure _PO2 (Pa) at a total pressure _PA = 10 Pa shown in Table 3-3 on the phosphorus removal rate (ΔP) of iron ore.

In developing the present invention, the inventors focused on lump ore having a high phosphorus concentration and low cost as a main raw material for metal smelting and metal refining, and studied a method for removing phosphorus from such a phosphorus-containing substance in advance. I recommended.

Iron ore used as a raw material for metal smelting and metal refining (main raw material and auxiliary raw material) is not produced in Japan, but is imported from overseas, such as Australia and Brazil. Large heavy machinery is used for mining at iron ore mines and is transported to steel company factories by rail, truck, ship, etc. In addition, transportation to the equipment using raw materials in the factory is carried out by unloaders, heavy machinery, conveyors, gas, and the like. In the process of such mining and transportation, the raw material is inevitably crushed and has a wide particle size distribution. Of these, iron ore of 10 mm or more is referred to as lump ore, and iron ore of less than 10 mm is referred to as powder ore. If necessary, the particle size is adjusted by a crushing facility such as a jaw crusher or a rod mill, and the classification process is performed using a sieve.

The method of transporting iron ore and the method of supplying it to equipment differ depending on the properties such as particle size and strength and the equipment used. For example, lump ore of 10 mm or more can be continuously transported by a conveyor or the like, but it is difficult to transport by gas. In addition, the method of adding lump ore often falls naturally due to its own weight, so it is directly charged from the upper part of the refining equipment using a conveyor or the like, or stored in a storage facility such as a hopper provided on the upper part of the refining equipment using a conveyor or the like. However, the required amount is cut out and charged when necessary.

Powder ore less than 10 mm can be transported by gas, but if it is transported by a conveyor or the like, it will be clogged and the transportation efficiency will be reduced. In addition, when the powdery raw material is naturally dropped by its own weight, the refining equipment is clogged due to dust scattering in the refining equipment, shelving occurs in the storage equipment such as a hopper, and the added powder ore is collected. Problems such as dusting and a decrease in the addition yield occur.

Based on the above, it is desirable to change the process and method of use for each particle size of the phosphorus-containing substance that has undergone phosphor nitriding removal. Even if the lump ore is directly charged as a raw material for a blast furnace, it is more expensive than the powder ore having the same composition because it can secure the air permeability required for the reduction of the ore. Table 1 shows an example of the composition of the lump ore.

Here, in order to express the iron content of iron ore, T.I. Although described in terms of the concentration of Fe, in reality, almost all of them exist in the form of Fe ₂ O ₃ . By the way, since phosphorus has a weaker affinity for oxygen than silicon (Si) and aluminum (Al), when a phosphorus-containing substance is reduced with carbon, silicon, aluminum or the like, it is contained in the phosphorus-containing substance. It is known that P ₂ O ₅ is easily reduced. On the other hand, since Fe ₂ O ₃ of iron oxide has the same affinity for oxygen as phosphorus, when the phosphorus-containing substance is reduced with carbon, silicon, aluminum, etc., Fe ₂ O ₃ is also reduced. become.

However, phosphorus has a high solubility in iron, and in particular, phosphorus produced by reduction is rapidly dissolved in iron produced by reduction to become high phosphorus-containing iron. As described above, the method for removing phosphorus by reduction has a problem that the phosphorus removal rate is low because phosphorus is adsorbed and dissolved in iron, which is a valuable component.

As a result of diligent research to solve this problem, the inventors removed phosphorus as a gas of phosphorus pentanitride (PN), and treated it at a temperature and oxygen partial pressure at which metallic iron and metallic manganese were not produced. It was found that it is possible to suppress the adsorption of phosphorus on iron and manganese.

That is, the inventors include the reaction (a) shown in the following chemical formula 1 for removing phosphorus existing as P ₂ O ₅ in the phosphorus-containing substance as a gas of phosphorus mononitride (PN), in the phosphorus-containing substance. It was confirmed by thermodynamic study that the iron oxide was reduced to metallic iron, which is more stable than the reaction (b) shown in the following chemical formula 2.

FIG. 1 shows the relationship between the temperature and the oxygen partial pressure when an equilibrium is established for the reaction (a) of the chemical formula 1. Further, for comparison, FIG. 1 also shows the relationship between the temperature and the oxygen partial pressure that can be achieved by the equilibrium between solid carbon and carbon monoxide gas (reaction (c) shown in Chemical Formula 3). Here, the P ₂ O ₅ activity is 0.001, the N ₂ partial pressure is 9.0 × 10 ⁴ Pa, the PN partial pressure is 1.0 × 10 ² Pa, the C activity is 1, and the CO partial pressure is 1. It was assumed to be 0.0 × 10 ⁴ Pa.

In FIG. 1, the reactions (a) and (c) proceed to the right in the temperature and oxygen partial pressure regions below the lines of the reactions (a) and (c), respectively. That is, in order to cause the phosphonitriding removal of the reaction (a), the oxygen partial pressure is 2.2 × 10 ^-14 Pa or less at 800 ° C., 1.45 × 10 ^-9 Pa or less at 1000 ° C., and 1200 ° C. It is necessary to have an oxygen partial pressure of 4.66 × ^10-6 Pa or less.

Here, in order to reduce the oxygen partial pressure, it is effective to coexist a simple substance such as an element stable as an oxide, for example, Ca, Mg, Al, Ti, Si, C, etc., but a simple substance of a metal element is effective. It is expensive. Therefore, in the present invention, from the viewpoint of reducing the processing cost, it is preferable to reduce the oxygen partial pressure by using carbon (C). It is also because, as can be seen from the description in FIG. 1, the oxygen partial pressure achieved by the solid carbon at a temperature of 724 ° C. or higher is a value sufficient to proceed with the nitriding removal reaction (a) of phosphorus. Recognize.

Further, in the reaction (a), when the amount of gas substance of the reactant and the product is compared, the amount of gas substance on the product side is large. In Le Chatelier's principle, in a reaction system in an equilibrium state, when a state variable is changed, the equilibrium moves in a direction that cancels the change. That is, when the total pressure of the reaction is reduced, the number of gas molecules is increased and the pressure is increased, that is, the reaction (a) proceeds to the right side, and it is possible to promote the target nitriding treatment. Conceivable.

<Experiment 1>
Next, based on the above-mentioned examination results, an experiment was conducted to confirm whether or not phosphonitriding could be removed. In this experiment, 10 g of iron ore whose particle size was adjusted to 1 to 3 mm was used as the phosphorus-containing substance, and 5 g of reagent carbon (particle size under 0.25 mm) was used as the solid carbon, and each was placed on a separate alumina boat. Then, it was allowed to stand in a small electric resistance furnace. After heating the furnace to a predetermined temperature (T = 600 to 1400 ° C.) while supplying Ar gas at 1 liter / min, the supply of Ar gas was stopped. After vacuuming to a predetermined pressure ( ¹⁰ to 105 Pa) or less with an oil rotary vacuum pump, the mixed gas of carbon monoxide (CO) and nitrogen (N ₂ ) is adjusted to a predetermined pressure P (Pa). While adjusting, it was held at a constant pressure and a constant temperature for 60 minutes. The ratio of the mixed gas of carbon monoxide and nitrogen was changed so that the nitrogen fraction _NN2 was in the range of 0.15 to 0.95 (corresponding to 15 to 95 vol% in volume fraction). Here, the nitrogen partial pressure _PN2 is represented by the product of the nitrogen fraction _NN2 and the total pressure _PA . After the lapse of a predetermined time, after the lapse of a predetermined time, the oil rotary vacuum pump is stopped, the supply of the mixed gas of carbon monoxide and nitrogen is stopped, the supply of Ar gas is switched to the supply of 1 liter / min, and the pressure reaches atmospheric pressure. After the pressure was restored, the temperature was lowered to room temperature, and the iron ore was recovered. In this experiment, the gas was supplied so that the side on which the reagent carbon was left to stand was upstream, so that the carbon monoxide gas and the reagent carbon reacted first.

As a result of conducting the above experiment at various nitrogen content, container pressure, temperature, and oxygen content, the phosphorus removal rate (ΔP = {(P concentration before the experiment)-" obtained from the composition analysis results of iron ore under the following conditions. It was confirmed that (P concentration after the experiment)} / (P concentration before the experiment)) (%) was high.
The nitrogen fraction _NN2 is preferably in the range of 0.2 or more and 0.9 or less.
The treatment temperature T (° C) should be 750 ° C or higher and 0.95 × T _m (° C) or less, and the oxygen partition coefficient PO2 (Pa) should be _logPO2 ≦ _-0.000025 × T ² +0.0723 × T-. It is preferable to satisfy the relationship of 58.8-0.4 × _logPA . Here, T _m is the melting temperature (° C.) of the phosphorus _- containing substance, and PA (Pa) is the total pressure in the reaction vessel.

The reason for this is that when the nitrogen fraction _NN2 is less than 0.2, the amount of nitrogen contributing to the reaction (a) is too small, and the nitriding removal of phosphorus by the reaction (a) does not proceed sufficiently within a predetermined treatment time. It is thought that this is because of it. On the other hand, when the nitrogen fraction _NN2 exceeds 0.9, the amount of CO gas supplied is small, and the oxygen partial pressure rises due to the oxygen generated by the thermal decomposition of iron oxide in the iron ore, resulting in the phosphorylated removal reaction (a). ) Is suppressed.

The reason why the treatment temperature T is less than 750 ° C. and the phosphorus removal rate is low is that, as shown in FIG. 1, the oxygen partial pressure required for phosphorus nitriding removal can be achieved by the reaction (c) with solid carbon at 724 ° C. or lower. It is thought that one of the reasons was that it was not. On the other hand, when the treatment temperatures T are 1350 ° C. and 1400 ° C., the iron ore is semi-melted to melted, and the recovered sample is integrated. As a result, the gaps and pores of the iron ore grains disappear. It is considered that the cause is that the boundary area in contact with the gas has decreased significantly. Regarding this point, the melting point (Tm) of iron ore measured by the differential thermal analysis method was 1370 ° C., and a high phosphorus removal rate was obtained at 1300 ° C., which is 0.95 times that, so the treatment temperature T was set to "0.95". It is considered preferable that the temperature is not more than × Tm (° C.) ”in order to secure the reaction boundary area for removing phosphorus.

In the above relational expression showing a preferable oxygen partial pressure _PO2 , the coefficient of the logarithmic influence term of the total pressure _PA is −0.4, which is a negative value. This means that the required oxygen partial pressure _PO2 may be higher as the total pressure _PA becomes smaller, and it means that the required treatment conditions are relaxed (for example, low temperature, low reduction atmosphere). do. It is considered that the reason for this is that the reaction (a) tends to proceed to the right side by reducing the total pressure _PA as described above. Here, the lower the total pressure PA is, the more effective it is, but in order to make it lower than 10 Pa, a plurality of or high _- performance and expensive vacuum pumps are required, so it is preferably 10 Pa or more.

The same method was applied to manganese ore and steelmaking slag, and experiments were attempted for different particle sizes. The range of fraction ( _NN2 ), the range of processing temperature T (° C) of "750 ° C or higher and 0.95 x _{TM (° C) or lower" (where T m is} the melting temperature of manganese ore or steelmaking slag), and , "Relational formula logP _O2 ≤ -0.000025 x T ² +0.0723 x T-58.8-0.4 x _{logPA A} " (where PA is the total pressure in the reaction vessel) It was found that a high phosphorus removal rate can be obtained by dividing the pressure _PO2 (Pa).

As described above, in order to remove phosphorus in a phosphorus-containing substance by nitriding, it is considered necessary to treat it at a predetermined pressure and temperature and supply nitrogen in an environment with a low oxygen partial pressure. The equipment for such processing may be any equipment such as an electric furnace, a rotary hearth furnace, a kiln furnace, a fluidized layer type heating furnace, a sintering machine, etc., which can raise the temperature and adjust the atmosphere. As a method for reducing the pressure inside the reaction vessel, the desired pressure inside the vessel is achieved, such as an oil rotary vacuum pump, a piston vacuum pump, a liquid-sealed vacuum pump, an ejector, a dry pump, an oil diffusion pump, and a turbo molecular pump. If possible, either method may be used.

Also, as a method of reducing the oxygen partial pressure,
(1) Bring the solid reducing agent into contact with nitrogen gas at high temperature.
(2) Mix reducing gas such as carbon monoxide, hydrogen, and hydrocarbon with nitrogen gas.
(3) Nitrogen gas is introduced into the solid electrolyte to which a voltage is applied to remove oxygen.
Any method may be used as long as a predetermined partial pressure of oxygen can be obtained.

According to the method of the present invention, low-phosphorus hot metal can be produced by blending iron ore treated with nitriding and dephosphorization as a low-phosphorus ingot ore in a blast furnace under a reduced pressure of less than atmospheric pressure. As a result, by reducing the amount of refining agent for hot metal pretreatment and ensuring a high hot metal temperature by shortening the treatment time, it became possible to use a large amount of cold iron source, which was effective in terms of energy saving and reduction of environmental load. Further, according to the method of the present invention, manganese ore treated with nitriding and dephosphorization was charged as a manganese source during converter refining under a reduced pressure of less than atmospheric pressure to melt low-phosphorus and high-manganese steel. In this method, low phosphorus and high manganese steel could be economically produced without using an expensive manganese alloy and without requiring a dephosphorization treatment in the subsequent treatment. Not limited to the above example, the method of the present invention can be applied to the pre-phosphorus removal treatment of recycled steel slag, auxiliary raw materials to be added in the pretreatment, and the like.

<Example 1>
The entire facility is sealed, and the amount of fuel and oxygen supplied to the heating burner by charging iron ore into a 5-ton / hr-scale rotary hearth furnace whose pressure inside the facility can be adjusted by a multi-stage steam ejector and its By adjusting the ratio and the amount of nitrogen gas to be supplied, the treatment temperature T is kept constant at 1000 ° C., and the nitriding treatment in which the total pressure _PA , nitrogen fraction _NN2 and oxygen partial pressure _PO2 in the facility are adjusted is performed for 30 minutes. Carried out. LPG was used as the burner fuel, and if necessary, an external heat type heater was used to adjust the temperature to a constant level. The temperature of the place where the charged sample was present after 15 minutes in the nitriding dephosphorization treatment and the gas composition analysis were performed. The carbon monoxide (CO) concentration (vol%) and carbon dioxide (CO ₂ ) concentration (vol%) in the gas were measured by an infrared gas analyzer, and the rest was treated as the nitrogen concentration (vol%). The nitrogen fraction _NN2 is {nitrogen concentration (vol%) / 100}. Further, the oxygen partial pressure _{PO2 was calculated from the measured value of the PCO / PCO2 ratio by} the calculation formula in the following chemical formula 4. The water ( _H2O ) generated by the burner combustion of LPG was separated by a drain before introducing the gas into the infrared gas analyzer. In addition, hydrogen (H ₂ ) was below the detection limit of the analyzer, and there was almost no unburned hydrogen.

Table 2 shows the processing conditions and the implementation results. As is clear from Table 2, the processing No. 1 to 9 have a total pressure PA in the range of 10 to 9.0 × 10 ⁴ Pa and a _nitrogen fraction _NN2 in the range of 0.20 to 0.90, and the phosphorus removal rate is in the range of 0.20 to 0.90 under any condition. It was as high as 70% or more. On the other hand, processing No. In 10, 12 and 14, the nitrogen fraction _NN2 was 0.15, and the phosphorus removal rate was as low as 30% at any of the total pressures. In addition, processing No. In 11, 13 and 15, the nitrogen fraction _NN2 was 0.95, and no phosphorus removal was confirmed. From the above results, it can be seen that in order to obtain a high phosphorus removal rate, it is preferable that the nitrogen fraction _NN2 is in the range of 0.2 or more and 0.9 or less.

When the nitrogen fraction _NN2 is below the lower limit, the amount of nitrogen in the atmosphere is insufficient, and it is probable that phosphorus could not be sufficiently removed within 30 minutes of this treatment time. On the other hand, when the nitrogen content _NN2 exceeds the upper limit, the amount of CO gas in the atmosphere, which is a reducing gas, is not sufficient, and oxygen generated by the thermal decomposition of iron ore and entrainment of iron ore from the inlet or the gap of the device. As a result of not being able to completely remove the oxygen contained in the air, it is probable that the oxygen partial pressure required for removing the nitride was not secured. This is consistent with the fact that almost no CO gas is detected in the gas analysis.

<Example 2>
Similar to Example 1, iron ore is charged into a 5 ton / hr scale rotary hearth furnace in which the entire equipment is sealed and the pressure inside the equipment can be adjusted by a multi-stage steam ejector, and the iron ore is supplied to a heating burner. By adjusting the amount and ratio of fuel and oxygen, and the amount of nitrogen gas to be supplied, the nitrogen fraction _NN2 is set to 0.9 constant, the total pressure _PA in the facility, the processing temperature T, and the oxygen partial pressure _PO2 . The nitriding treatment was carried out for 30 minutes. The method for calculating the oxygen partial pressure is the same as in Example 1.

Tables 3-1 to 3-3 show the processing conditions and results when the pressures in the equipment were 9.0 × 10 ⁴ Pa, 1.0 × 10 ³ Pa and 10 Pa, respectively. 2 to 4 show the relationship between the treatment temperature T (° C.) and the oxygen partial pressure _PO2 (Pa) shown in Tables 3-1 to 3-3, respectively. In FIGS. 2 to 4, the results with a phosphorus removal rate of 70% or more (treatments No. 16 to 25, 37 to 46 and 58 to 67) are marked with ◯, and the results with a phosphorus removal rate of less than 10% (treatments No. 26 to 26). 36, 47-57 and 68-78) were plotted with x.

As is clear from Tables 3-1 to 3-3 and FIGS. 2 to 4, the treatment temperature T (° C.) is in the range of 750 ° C. or higher and 0.95 × T _m (° C.) or lower, and the oxygen partial pressure _PO2 ( It can be seen that a high phosphorus removal rate is obtained when Pa) satisfies the relationship of logP _O2 ≤ −0.000025 × T ² +0.0723 × T-58.8-0.4 × logPA _A. The following reasons can be considered as the reason why the phosphorus removal rate was low when the above conditions were not met. Processing No. 26 to 28, 47 to 49 and 68 to 70 are treatments at a treatment temperature T of 700 ° C. or lower, and the oxygen partial pressure determined from the CO-CO ₂ equilibrium shown in Chemical Formula 4 is the low required for nitriding removal of phosphorus. It is probable that the oxygen partial pressure was not reached. On the other hand, processing No. 34 to 36, 55 to 57 and 76 to 78 were treated at 1400 ° C. and the melting temperature of the iron ore of the sample was T _m = 1370 ° C. or higher, so that the sample was melted and the internal pores were formed. It is considered that the boundary area was significantly reduced as a result of the disappearance of the gaps between the grains. In addition, processing No. For 29 to 33, 50 to 54 and 71 to 75, the treatment temperature range is suitable, but the oxygen partial pressure does not satisfy the above-mentioned suitable conditions, and the low oxygen partial pressure required for nitriding removal of phosphorus cannot be achieved. It is thought that it was.
It was confirmed that a high phosphorus removal rate can be obtained when the nitrogen fraction, the treatment temperature and the oxygen partial pressure satisfy the above-mentioned preferable conditions even when the treatment time is changed by using the same equipment.

When phosphorus is to be removed in steel smelting, quicklime, slaked lime, dolomite, etc. containing CaO are added as a refining agent to generate slag. Dephosphorization refining is usually carried out under oxidizing conditions, and iron is also oxidized at the same time, so that iron is taken into the slag, iron loss occurs, and the yield decreases. Further, steel refining is performed at a high temperature of 1300 to 1700 ° C., and the slag needs to be at the same temperature, so that energy loss also occurs.

Generally, in order to remove phosphorus equivalent to a P concentration of 0.001 mass% from hot metal, it is necessary to add 200 to 250 g / t-hot metal in terms of CaO when dephosphorizing by pretreatment, and iron. The amount of loss is 75 to 100 g / t-hot metal. On the other hand, similarly, when dephosphorizing by converter decarburization, it is necessary to add about 450 g / t-hot metal in terms of CaO, and the amount of iron loss is 200 g / t-hot metal.

As described above, in order to remove phosphorus in steel refining, a large amount of auxiliary raw material addition and energy are required. In the present invention, phosphorus-containing substances used as raw materials for steel smelting and steel refining processes are reacted with nitrogen-containing gas to remove phosphorus in the phosphorus-containing substances by nitriding, thereby in steel smelting and steel refining processes. The phosphorus concentration is reduced, and low-phosphorus steel can be smelted without the need for adding a large amount of auxiliary raw materials or energy as described above.

The technique disclosed in the present invention is not limited to the above iron ore, and can be applied to a main raw material or an auxiliary raw material for metal smelting and metal refining such as manganese ore and steelmaking slag. It is also possible to recycle the removed phosphorus pentanitride ₍ PN) in the exhaust gas as P2O5 _- containing dust or the like as a phosphoric acid fertilizer.

Claims (5)

A method for removing phosphorus in a phosphorus-containing substance by reacting a phosphorus-containing substance used as a raw material for metal smelting or metal refining with a nitrogen-containing gas having a nitrogen content of _NN2 that satisfies the conditions of the following formula 1. And
The total pressure PA (Pa) of the atmosphere is reduced to less than atmospheric pressure, and the phosphorus _- containing substance is subjected to the conditions of the following formula 2 (in the formula, Tm _represents the melting temperature (° C.) of the phosphorus-containing substance). Phosphorus is characterized in that at least a part of phosphorus is removed from the phosphorus-containing substance by heating to a treatment temperature T (° C.) to be satisfied and reacting with the nitrogen-containing gas to generate phosphorus mononitride (PN). A method for removing phosphorus from contained substances.

The method for removing phosphorus from a phosphorus-containing substance according to claim 1, wherein the nitrogen-containing gas has an adjusted oxygen partial pressure _PO2 (Pa). The method for removing phosphorus from a phosphorus-containing substance according to claim 2, wherein the nitrogen-containing gas contains a reducing gas. The method for removing phosphorus from a phosphorus-containing substance according to claim 2 or 3, wherein the oxygen partial pressure _PO2 (Pa) in the nitrogen-containing gas satisfies the condition of the following formula 3.

A method for producing steel, which is contained by the method for removing phosphorus from a phosphorus-containing substance according to any one of claims 1 to 4 in at least one of a metal smelting step and a metal refining step. A method for producing steel, which comprises using iron ore or manganese ore from which a part of phosphorus is removed as at least a part of a raw material to produce steel.

Images