JP2008163463A - Method for reducing chromium-metal from chromium oxide-containing slag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reducing a chromium-metal from a chromium oxide-containing slag with which the chromium contained in a stainless slag in an electric furnace can efficiently be reduced and recovered into a low concentration thereof. <P>SOLUTION: In a process reducing the chromium contained in the electric furnace slag during a stainless steel-making process, while maintaining the slag as the liquid-state, the charging quantity of powdery aluminum dross is in the range of 10-20 kg per 1 ton of molten steel, or the Al dross is injected into the electric furnace slag so as to satisfy the following formula, 0.5≤[Al dross charging quantity (ton)×100]/[electric furnace slag quantity (ton)×Cr<SB>2</SB>O<SB>3</SB>concentration (%)]≤1.0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for reducing chromium metal from oxidized chromium slag, and more specifically, when recovering valuable metals such as chromium contained in electric furnace slag during a stainless steel making process, the recovery rate can be improved. As described above, the present invention relates to a method for reducing chromium metal from oxidized chromium slag by blowing powder aluminum dross.

  Generally, a steelmaking process including a refining process of stainless steel includes an electric furnace, a refining furnace, fine adjustment of components, and a continuous casting process. Moreover, in order to flexibly cope with the market demand for stainless steel, production methods including an electric furnace are more widely used.

  The production of molten steel by an electric furnace is roughly divided into a method of melting scrap and alloy iron and a method of mixing and melting molten iron and scrap. However, in the case of high-grade steel such as stainless steel, in consideration of quality, a method of melting in an electric furnace using only high-grade scrap and alloy iron with a lower impurity content is the mainstream. . However, in this case, since the cost burden is higher than when using a hot metal with a low price, it is necessary to efficiently reduce and recover by-products containing valuable metals such as chromium. Various methods have been proposed. In particular, in the case of chromium, since it is eluted in the form of hexavalent chromium, there is a problem of causing environmental pollution, so it must be removed from the slag.

  Stainless steel contains 10% or more chromium component due to the characteristics of the component, and since the chromium component has a higher affinity with oxygen than iron (Fe), the steelmaking process is performed at a high temperature of 1500 ° C or higher. Then, oxidation of the chromium component inevitably occurs.

  In addition, in the case of an electric furnace, oxygen is essentially blown in order to promote melting of scrap, so that a large amount of chromium components are oxidized and slag is formed during the production of molten stainless steel.

  In the production process of stainless steel using an electric furnace, the chromium oxide content in the slag generated as a by-product is a high level of about 5% to 30%. Therefore, in order to reduce manufacturing costs or use resources more efficiently, silicon iron (Fe—Si) and aluminum are heated within the heating period when the temperature of the molten steel is increased after the alloy iron and scrap are melted. It is common to add a reducing agent such as to reduce chromium oxide in slag into molten steel.

  Chromium oxide in the slag existing during the heat-up period is partially reduced by silicon (Si) or carbon, which is a component in the molten steel. However, in general, in order to raise the temperature of the molten steel while reducing the power consumption of the electric furnace, a large amount of oxygen is blown into the molten steel during the heat-up period, so the amount of chromium reduction by silicon or carbon in the molten steel is oxygen Compared to the amount of oxidation by

  Further, in the case of silicon iron or aluminum used as a reducing agent, since the price is high, the amount of use is constrained, and conversely, it may cause an increase in cost. For this reason, there has been an attempt to suppress the oxidation of chromium during the blowing of oxygen.

  In Korean Published Patent No. 2005-0109763 (Patent Document 1), when recovering valuable metals in a stainless steel electric furnace slag, the temperature of the slag is increased by using a burner. A method of maintaining an advantageous high temperature liquid state is disclosed. However, chromium oxidation can be suppressed by this method, but since a reducing agent is essential, the effect is not great. The slag that has not undergone such a separate reduction process is discharged together with molten steel and discharged, and chromium can be recovered only through a separate process other than the steelmaking process.

  In Japanese Patent Laid-Open No. 2001-316712 (Patent Document 2), at least one of the electrodes of an electric furnace is a hollow electrode, and a reducing agent such as aluminum, aluminum dross, or carbon is not introduced through the hollow electrode. A method of reducing chromium oxide in slag by blowing with an active gas is disclosed. Since this method uses a hollow electrode, its application is limited.

  Korean Patent Publication No. 2000-0021329 (Patent Document 3) discloses a method for inducing recovery of valuable metals and slag forming by blowing powdered carbon into an electric furnace. However, in this case, there is a problem that the reaction between chromium oxide and carbon hardly occurs at a low temperature and the reduction rate is slow.

  Also, Korean Published Patent No. 1998-047211 (Patent Document 4) discloses a method of recovering chromium by gas stirring in a ladle after tapping the electric furnace. However, this method has a disadvantage that the loss of chromium in the slag discharged during the hot water is large. The post-treatment for recovering valuable metals from the waste slag is expensive and time consuming, such as crushing, water selection, magnetic separation, flotation, etc. One of the factors. Therefore, it is very advantageous in terms of economy to recover as much chromium as possible from the molten slag before discharging.

Generally, before tapping molten steel made in an electric furnace, silicon iron (Fe-Si) alloy in the range of 2kg to 3kg per ton of molten steel is introduced, and a part of valuable metals including chromium is obtained by the following reaction. Collected.
(Reaction Formula 1)
(Cr ₂ O ₃ ) + [Si] = (SiO ₂ ) + [Cr]
(Reaction Formula 2)
(MnO) + [Si] = (SiO ₂ ) + [Mn]
(Reaction Formula 3)
(FeO) + [Si] = (SiO ₂ ) + [Fe]

The silicon iron alloy thrown into the molten steel of the electric furnace increases the silicon content by dissolving in the molten steel. This reduces chromium in the slag by the interfacial reaction between the molten steel and the slag. However, when silicon iron is used as a reducing agent, most silicon is oxidized by oxygen blown into the molten steel. Therefore, silicon used for chromium reduction does not reach 50% of the input. In addition, when adding a large amount of silicon in order to increase the recovery rate of chromium in the slag, a large amount of silicon oxide (SiO ₂ ) is generated, so that the basicity of the slag (CaO / SiO ₂ ) is lowered and the flow of the slag Worsens sex. Accordingly, the working efficiency is lowered, which is a disadvantageous condition when the chromium oxide in the slag is reduced.

In order to reduce the manufacturing cost of stainless steel, in order to increase the recovery rate of valuable metals including expensive chromium, it is a fact that the use of a reducing agent having higher efficiency than conventional silicon iron is required.
Korean Published Patent No. 2005-0109763 Japanese Unexamined Patent Publication No. 2001-316712 Korean Published Patent No. 2000-0021329 Korean Published Patent No. 1998-047211

  Therefore, the present invention is an invention made to solve the conventional problems as described above, and its purpose is to efficiently reduce and recover chromium contained in a stainless steel electric furnace slag to a low concentration. It is an object of the present invention to provide a method for reducing chromium metal from oxidized chromium-containing slag.

  In order to achieve the above object, the method for reducing chromium metal from oxidized chromium-containing slag according to the present invention maintains the slag in a liquid state in the step of reducing chromium contained in the electric furnace slag during the stainless steel making process. , The amount of powdered aluminum dross is in the range of 10-20 kg per ton of molten steel, or

Inject into the electric furnace slag to satisfy the equation.

  Preferably, when the powdered aluminum dross is blown, the particle size thereof is in the range of 1 mm to 5 mm, together with at least one inert gas of nitrogen (N) or argon (Ar) gas, through a mild steel pipe. Infuse. The blowing amount is blown in an amount equal to or more than the chemical equivalent for reducing chromium in the slag. Further, the blowing of the powdered aluminum dross is performed at the time when the blowing of oxygen is finished during the operation of the electric furnace or when the electric power of the electric furnace is in the range of 300 kW / ˜400 kW / ton. Is adjusted to a range of 1.1 to 1.7, and the alumina content in the slag is maintained at 10% or more.

Further, the method for reducing chromium metal from oxidized chrome slag according to the present invention comprises reducing the chromium in the slag of the electric furnace to an aluminum component by blowing powder aluminum dross, and in the powder aluminum dross Adjusting the alumina (Al ₂ O ₃ ) component and slag basicity to increase the slag fluidity of the electric furnace.

  Here, the step of reducing the valuable metal in the slag of the electric furnace to the aluminum component in the powder aluminum dross has a particle size of the powder aluminum dross in the range of 1 mm to 5 mm, and the blowing amount is set in the slag. The chemical equivalent of reducing chromium is set to be equal to or more than that, and the timing of blowing the powder aluminum dross is set to the time when the blowing of oxygen is completed, or the range of the integrated electric power of the electric furnace from 300 kW / ton to 400 kW / ton. The powder aluminum dross is blown by inserting a mild steel pipe into the slag and using at least one inert gas of nitrogen (N) or argon (Ar) as a carrier. Moreover, the step of increasing the slag fluidity adjusts the basicity of the electric furnace slag to a range of 1.1 to 1.7, and the alumina concentration in the slag is 10% or more. And

  On the other hand, in the non-ferrous field, during the refining of aluminum, it is preferable to industrially use aluminum dross generated in a considerable amount as a refining slag in terms of utilization of waste and environmental considerations.

  As described above, according to the chromium metal reduction method from the oxidized chromium slag of the present invention, the reduction of chromium oxide contained in the stainless steel electric furnace slag and the recovery rate of chromium are increased by blowing aluminum dross. be able to. And the cost of a stainless steel manufacturing process can be reduced by using powder aluminum dross which is cheaper than the conventional reducing agent.

  Below, with reference to drawings which show the example of the present invention, the chromium metal reduction method from oxidation chromium slag concerning the present invention is explained concretely.

  FIG. 1 is a schematic diagram showing a typical stainless steel electric furnace (EAF) process, and FIG. 2 is a graph showing the loss rate of chromium in the slag during the stainless steel electric furnace process.

  As shown in FIG. 1, the electric furnace operation generally has two to three raw material charging steps. This is because scrap iron is tens of times larger than dissolved iron. At the time of primary charging, scrap iron and alloy iron corresponding to about 50% of the amount of hot water are put into an electric furnace and then energized to perform primary melting. Thereafter, the energization is stopped, the electric furnace loop is opened, and the remaining scrap iron and alloy iron are secondarily charged. Subsequently, when the current is re-energized, and the scrap iron and the alloy iron are completely dissolved, the amount of power is reduced. Then, oxygen is blown in and the hot water is discharged through a heat-up period in which the temperature of the dissolved iron is raised to a target value.

  During the operation of the electric furnace described above, the molten metal is always in contact with the atmosphere, so that chromium is oxidized and the molten steel component is lost. Therefore, silicon iron (FeSi) is used as these reducing agents, but nevertheless, as shown in FIG. 2, loss of chromium occurs in the form of slag, skull, dust, and the like. Of these, the proportion of the portion where the oxidized chromium flows into the slag and is lost is absolutely large, and it is urgently required to recover the valuable metal by reducing it.

  In order to maximize the recovery of valuable metals in the slag, it is necessary to consider not only the performance and shape of the reducing agent, but also the slag composition with excellent fluidity and the temperature of the molten steel.

First, chromium oxide contained in slag can be reduced thermodynamically by the aluminum component in aluminum dross.
(Reaction Formula 4)
(Cr ₂ O ₃ ) + 2Al (l) = 2Cr (s) + (Al ₂ O ₃ )
(Reaction Formula 5)
3 (MnO) + 2Al (l) = 3Mn (l) + (Al ₂ O ₃ )
(Reaction Formula 6)
3 (FeO) + 2Al (l) = 3Fe (l) + (Al ₂ O ₃ )

  As a result, valuable metal oxides contained in the slag of a stainless steel electric furnace are reduced by causing the above reaction when contacting with aluminum at a temperature (about 1600 ° C) at which molten steel and slag are formed. Can be done. However, in the stainless steel electric furnace operation, the melting time is shortened as much as possible in consideration of productivity, so that the actual application becomes difficult when the reaction rate is slow.

  Such a reduction reaction rate of the element in the slag is proportional to the mass transfer rate of the valuable metal oxide in the slag and the contact area between the reduction material. Therefore, an increase in mass transfer rate due to slag agitation or an increase in reaction area due to an increase in the surface area of aluminum dross acts as an important factor in increasing the reduction rate of valuable metals.

  In order to increase the reaction area, it is a good means to increase the surface area of the blown carbon, and for this purpose, a powder with a small particle size must be used.

  Therefore, in view of the reaction rate, when the particle size of aluminum dross is 5 mm or more, it is disadvantageous than aluminum dross having a smaller particle size. Further, other components other than aluminum present in the aluminum dross may react with the slag according to the content thereof and change the physical properties of the slag, thereby preventing the reduction of chromium oxide. Therefore, the smaller the content of the aluminum component that serves as a reducing agent, the more disadvantageous the reduction reaction. Therefore, in the examples of the present invention, the content of the aluminum component in the aluminum dross was limited to 30% or more, and the particle size was limited to a range of 1 mm to 5 mm.

  FIG. 3 is a diagram illustrating a change in viscosity of slag according to the slag composition.

As shown in the above reaction, the alumina (Al ₂ O ₃ ) component generated when valuable metal oxides are reduced by aluminum plays a role in decreasing the viscosity of slag and increasing fluidity, as shown in FIG. Fulfill. Thereby, the mass transfer rate of the oxide can be increased, and the reduction reaction rate can be further increased.

  On the other hand, in order to blow powder aluminum dross into the slag layer and make it come into contact with the oxide, an inert gas (nitrogen or argon) having no ignitability must be used, and further, depending on the depth of the slag. In order to withstand the pressure, a gas pressure above a certain level is required. In the present invention, a powdered aluminum dross blowing mild steel pipe is inserted from the work opening toward the furnace center where the electrode is provided, and a 2 inch mild steel pipe is formed by using nitrogen gas in the range of 3 bar to 4 bar. Was blown into the slag.

  FIG. 4 is a plan view showing a mild steel pipe for injecting powder aluminum dross in an electric furnace according to the present invention.

  As shown in the figure, the position where aluminum dross is blown in the electric furnace 1 is not the oxygen blowing pipe 3 but the powdered aluminum dross blowing mild steel pipe 4. Then, along with the powdered aluminum dross, argon or nitrogen gas is blown to promote slag stirring, thereby increasing the reduction reaction rate. The electric furnace 1 has an electrode 2 but is composed of three upper electrode rods. After the scrap iron is charged into the electric furnace 1, a current is passed therethrough and a high heat such as arc heat generated at this time. The scrap iron is melted at

  Generally, in order to obtain molten steel at a constant temperature by melting scrap in an electric furnace, an input power of about 420 kW / ton is required in the case of stainless steel. For example, when scrap and alloy iron are melted in an electric furnace having a capacity of 90 tons, an input power of 300 kW / ton is used for melting of scrap and alloy iron, and then 120 kW / ton of power is used for melting steel and slag. Is used to raise the temperature to 1600 ° C.

  The former period is called the dissolution period, and the latter period is called the heating period. In order to reduce chromium in the slag, a reducing agent must be added during the heat-up period, but during the heat-up period, oxygen is blown to reduce the input power and promote stirring of the slag and molten steel. Therefore, it is preferable to delay the charging time of the reducing agent as much as possible. In the case of other reducing agents, sufficient reaction time is required until the slag and the reducing agent come into contact with each other and a valuable metal reduction reaction occurs. However, since the reduction reaction of chromium by aluminum occurs very fast in terms of speed, a sufficient reduction reaction can be expected even if the input timing is delayed to the point when the oxygen blowing is finished.

  In order to make the input amount of aluminum dross more than the chemical equivalent for reducing chromium in the slag, it is preferable to satisfy the range of 10 to 20 kg per ton of molten steel, or (Equation 3).

On the other hand, in order to increase the reaction rate between slag and aluminum dross, the slag must maintain a liquid state and the fluidity (viscosity) of the slag must be sufficiently ensured. As shown in FIG. 3, the fluidity of the slag is highest when the basicity (CaO / SiO ₂ ) is in the range of 1.1 to 1.7 and the alumina content of the slag is 10% or more. The fluidity of such slag not only increases the reaction rate, but also helps reduce the valuable metal to be absorbed into the molten steel, thereby preventing it from being collected and rejected by the slag. .

  Examples of the present invention will be described below.

Example Comparison of reduction of chromium oxide in slag by use of silicon iron generally used in stainless steel electric furnace and reduction by powdered aluminum dross presented in the present invention in actual operation did.

  In general, in a stainless steel electric furnace, after melting of scrap and alloy iron, the chromium content in the slag before reduction reaches a range of 20% to 25%. As described above, this is a result of oxidation of the chromium component in the molten steel due to atmospheric contact with the molten steel being operated or oxygen blowing. In the Example of this invention, the effect of this invention was verified by comparing the case where such a chromium component is reduce | restored to the silicon iron which is a conventional method, and the case where it reduces to powder aluminum dross.

The following (Table 1) shows a comparison of the Cr ₂ O ₃ content in the slag of the present invention and the prior art.

  Referring to (Table 1), as a result of blowing powder aluminum dross, the content of chromium oxide remaining in the slag after tapping of the electric furnace stainless steel molten steel is in the range of 2% to 5%, and conventional silicon iron is used. It can be seen that chromium oxide in the range of 2% to 8% is further reduced as compared with the reduction method.

  FIG. 5 is a graph showing the chromium oxide content remaining in the slag during the reduction of chromium by the method of the present invention in comparison with the conventional one.

  First, when using silicon iron (3 kg per ton of molten steel), which is a general method for reducing valuable metals, the content of chromium oxide remaining in the slag after hot water is analyzed. As shown, it reaches the range of 7% to 10%. In this case, the injection time of silicon iron is the end of the blowing of oxygen and can be said to be the injection time to maximize the reduction effect by silicon iron, but the residual chromium oxide content is at a very high level.

  However, the amount of powder aluminum dross blown when the powder aluminum dross presented in the present invention is blown is 10 kg per ton of molten steel, and the time required for blowing varies depending on the pressure of nitrogen. However, in the range of nitrogen pressure 3 bar to 4 bar, it takes about 10 minutes. The start time of blowing is the end of blowing oxygen. This is to maximize the reduction effect and prevent oxidation of aluminum by oxygen.

  Therefore, when the powder aluminum dross according to the present invention is blown, the reduction of chromium oxide and the recovery rate of chromium can be improved compared to the reduction of chromium using conventional silicon iron.

  Although the technical idea of the present invention has been specifically described by the preferred embodiments as described above, it is well known that the above embodiments are for the purpose of illustration and not for limitation. Must. Moreover, those skilled in the art of the present invention will understand that various embodiments are possible within the scope of the technical idea of the present invention.

It is a schematic diagram which shows a general stainless steel electric furnace process. It is a graph which shows the loss rate of the chromium in slag in a stainless steel electric furnace process. It is a figure which shows the viscosity change of slag according to a slag composition. It is a top view which shows the mild steel pipe for powder aluminum dross blowing of the electric furnace which concerns on this invention. It is a graph which shows the chromium oxide content which remains in slag at the time of reduction | restoration of chromium by the method of this invention compared with the conventional one.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Electric furnace 2; Electrode 3; Oxygen blowing pipe 4; Mild steel pipe for powder aluminum dross blowing

Claims (9)

In the process of reducing chromium contained in the electric furnace slag during the stainless steel making process,
A method for reducing chromium metal from oxide-containing chromium slag, wherein the amount of powdered aluminum dross is blown into an electric furnace slag so as to satisfy the following formula while maintaining the slag in a liquid state.

In the process of reducing chromium contained in the electric furnace slag during the stainless steel making process,
A method for reducing chromium metal from oxidized chromium slag, characterized in that the amount of powdered aluminum dross is blown into the electric furnace slag while maintaining the slag in a liquid state in a range of 10 kg to 20 kg per ton of molten steel.   3. The method for reducing chromium metal from oxidized chromium slag according to claim 1, wherein a particle size of the powdered aluminum dross is in a range of 1 mm to 5 mm.   The powdered aluminum dross is blown through a mild steel pipe together with at least one inert gas of nitrogen (N) or argon (Ar) gas from the oxidized chrome slag according to claim 3. Of chromium metal reduction.   The said powder aluminum dross blows the quantity more than the chemical equivalent which reduces the chromium in slag, The chromium metal reduction method from the oxygen-containing chromium slag of Claim 4 characterized by the above-mentioned.   The method for reducing chromium metal from oxidized chrome slag according to claim 1 or 2, wherein the blowing of the powdered aluminum dross is performed at the time when the blowing of oxygen is finished during operation of the electric furnace.   The powdered aluminum dross is blown in an electric furnace during operation of the electric furnace at a time in the range of 300 kW / ton to 400 kW / ton of accumulated electric power of the electric furnace. From chromium metal reduction.   The basicity of the electric furnace slag is in the range of 1.1 to 1.7, and the method for reducing chromium metal from oxidized chrome slag according to claim 1 or 2.   The method for reducing chromium metal from oxidized chromium slag according to claim 8, wherein the alumina content in the electric furnace slag is maintained at 10% or more.

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