JP2022046417A - Method for producing chromium-containing molten iron - Google Patents

Abstract

To provide a method for producing chromium-containing molten iron which is inexpensive and generates little waste.SOLUTION: A method for producing chromium-containing molten iron comprises dissolving a raw material containing chromium-containing raw material and roughly decarburizing the raw material by blowing oxygen using an electric furnace for steelmaking. The method comprises a first step in which molten iron is discharged while chromium oxide-containing slag produced by blowing oxygen remains in the furnace after adjusting the basicity of the slag within a range from 1.5 to 1.7 or from 1.9 to 3.5, and a second step in which the remaining chromium oxide-containing slag is reduced by a carbon source or a metal source newly added in the same furnace and chromium is recovered in molten iron. Here, the basicity of the slag is obtained by dividing the CaO concentration by the SiO2 concentration on the basis of the mass in the slag.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing chromium-containing molten iron using an electric furnace for steelmaking.

In the chromium-containing molten iron refining process, after the raw material containing the chromium-containing raw material is melted, oxygen is supplied to perform decarburization and blowing, and after the oxygen is blown off, a reducing material such as a Si-containing raw material or an Al-containing raw material is added. By doing so, the mainstream method is to recover the valuable metal chromium content in the molten iron from the chromium oxide generated at the same time as the oxidation of carbon, and then discharge the hot water.

In order to reduce the produced chromium oxide, a chemical equal amount of reducing agent is required, and an expensive Si alloy or Al alloy is required in a considerable amount. In addition to the above, it is also necessary to add CaO to adjust the slag composition for SiO ₂ and Al ₂ O ₃ generated during the reduction of chromium oxide, which increases the lime cost and the amount of generated slag. Invite an increase. In particular, since the slag generated in this step has a certain amount of chromium oxide concentration, there is a problem that hexavalent chromium may be eluted when used as a roadbed material or an aggregate as a by-product.

In order to reduce the amount of the Si-containing raw material or the Al-containing raw material used, a method of terminating the treatment without reducing the chromium oxide-containing slag and separately using a hot metal or a carbon-containing raw material to reduce the slag has been studied. For example, Patent Document 1 discloses a method of recovering chromium in molten iron by removing or removing slag without reducing it after oxygen blowing and reducing the slag with carbon or silicon in an electric furnace. Has been done.

Further, in Patent Document 2, after the chromium oxide-containing slag is generated, hot water is discharged without reduction, and the hot metal is charged into the smelting furnace to add carbonaceous material and blow acid to recover chromium in the molten iron. The method of doing so is disclosed.

Further, in Patent Document 3, after the chromium oxide-containing slag is produced, calcium carbonate is added without reduction to solidify the slag, so that only molten iron is discharged and the chromium oxide-containing slag is separately discharged to generate electricity. A method of recovering chromium in molten iron by charging it into a furnace and reducing it is disclosed.

Japanese Unexamined Patent Publication No. 2013-79449 Japanese Unexamined Patent Publication No. 2002-256323 Japanese Unexamined Patent Publication No. 2012-21372

However, the above-mentioned prior art has the following problems.
In the method described in Patent Document 1, it is necessary to recharge the slag containing chromium oxide into another refining container after slagging, which causes a problem that heat loss is large and electric power cost or heat heating cost of carbonaceous material is large. was there.

Further, in the method described in Patent Document 2, there is a problem that the slag adheres to the furnace wall, the furnace mouth, and the vicinity of the hot water hole when the slag containing chromium oxide remains and is discharged, resulting in deterioration of the operation. rice field. Especially in electric furnaces, unlike pot containers and converter type reaction vessels equipped with mechanical stirring that can operate with slag with a high solid phase ratio, it is difficult to increase the stirring power and ensure the fluidity of slag. It is difficult to do.

Further, in the method described in Patent Document 3, the problem of slag fixation can be solved by solidifying the slag containing chromium oxide, but the decomposition reaction of calcium carbonate is an endothermic reaction, and the temperature of the slag is lowered. Therefore, there is a problem that the power cost or the heat heating cost of the carbonaceous material becomes large in the slag recovery process.

The present invention has been made in view of such circumstances, and an object of the present invention is to propose a method for producing chromium-containing molten iron which is inexpensive and produces less waste without affecting the operation.

As a result of repeating various experiments in order to solve the above problems, the inventors focused on the fact that the solid phase ratio and viscosity of the chromium oxide-containing slag after oxygen supply greatly change depending on its basicity, and chromium oxidation By leaving the substance-containing slag in the furnace and reducing it with a carbon source or metal source newly added in the same refining furnace, chrome-containing molten iron that is inexpensive and produces less waste without affecting the operation can be obtained. It was found that it can be manufactured. The present invention has been made based on the above findings, and the gist thereof is as follows.

The method for producing chromium-containing molten iron of the present invention, which advantageously solves the above problems, is a method for producing chromium-containing molten iron, which uses an electric furnace for steelmaking to melt raw materials including chromium-containing raw materials and to perform crude decarburization by blowing oxygen. In the manufacturing method, after adjusting the basicity of the slag to the range of 1.5 or more and less than 1.7 or 1.9 or more and 3.5 or less, the chromium oxide-containing slag produced by blowing oxygen is placed in the furnace. The first step of discharging hot water while leaving it in the same furnace, and the second step of reducing the slag containing chromium oxide remaining by the carbon source or metal source newly added in the same furnace and recovering the chromium in the molten iron. Here, the basicity of the slag is characterized by dividing the CaO concentration by the SiO ₂ concentration on the basis of the mass in the slag.

The method for producing chromium-containing molten iron according to the present invention is as follows.
(1) In the first step, the chromium oxide concentration in the slag is 5 mass% or more and 50 mass% or less by using one or two selected from the Si-containing raw material and the Al-containing raw material after oxygen is blown. To adjust,
(2) In the first step, slag and metal particles adhering to the furnace wall are added onto molten iron by dropping them after oxygen is blown.
Etc. may be a more preferable solution.

According to the present invention, chromium oxide-containing slag remains in the furnace without affecting the operation and is reduced by a carbon source or a metal source newly added in the same refining furnace, so that the slag is inexpensive and produced. It is possible to produce chromium-containing molten iron with less slag, which contributes to the reduction of environmental load.

It is a basic block diagram of the manufacturing method of chromium-containing molten iron which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the basicity of the slag and the basicity of the liquid phase to be formed at 1700 ° C. calculated by using the thermodynamic calculation software for each chromium oxide concentration in slag.

The idea that led to the discovery of the present invention will be described.
The melting point of chromium oxide is as high as 2300 ° C. The temperature of the chromium oxide-containing slag after supplying oxygen to the chromium-containing molten metal is about 1700 ° C., and since it contains a large amount of chromium oxide, the liquid phase ratio is low and the viscosity is very high. Therefore, when only molten iron is discharged without reducing the chromium oxide-containing slag, a large amount of the slag remains as fixed slag near the furnace wall, the furnace mouth, or the hot water hole, which hinders the operation.

For example, in a relatively small-volume furnace such as an electric furnace, the slag attached during tilting may block the path of oxygen gas from the acid feed lance, or the slag may block the hot water outlet hole when hot water is discharged. Such an operation obstruction occurs.

Therefore, the inventors have stated that the adhesive force of slag to the furnace body is greatly affected by the viscosity of the liquid phase portion of the slag, and that the basicity of the chromium oxide-containing slag in an oxidizing atmosphere is 1. We focused on the fact that the solid phase ratio is locally high in the range of 7 or more and smaller than 1.9, and that a slag state with low viscosity can be secured in the high basicity region. Then, he found a method for leaving the chromium oxide-containing slag in the furnace without affecting the operation. That is, we have developed a method for producing chromium-containing molten iron that is inexpensive and produces less slag by reducing it with a carbon source or a metal source newly added in the same refining furnace.

FIG. 1 shows a basic configuration flow chart of a method for producing chromium-containing molten iron according to an embodiment of the present invention. First, as a first step, a raw material containing a chromium-containing raw material is melted (S0) using an electric furnace for steelmaking, and rough decarburization (S1) is performed by blowing oxygen. In this first step, the basicity of the slag is adjusted within the range of 1.5 or more and less than 1.7 or 1.9 or more and 3.5 or less, and then the chromium oxide-containing slag produced by blowing oxygen is used. Leave the hot water in the furnace (S2). Here, the basicity of the slag is based on the mass in the slag, and the CaO concentration is divided by the SiO ₂ concentration.

Next, as a second step, the chromium oxide-containing slag remaining in the furnace is reduced by a carbon source or a metal source newly added in the same furnace, and chromium is recovered in the molten iron (S3). ) Therefore, chromium-containing molten iron can be effectively produced.

In the first step, the chromium oxide (Cr ₂ O ₃ ) concentration in the slag is reduced to 5 mass% or more and 50 mass% or less by using one or two kinds selected from the Si-containing raw material and the Al-containing raw material after oxygen injection. By carrying out the weak reduction step (S4) to be adjusted, chromium-containing molten iron can be produced more stably. Further, by carrying out the step (S5) of pushing in the slag and metal particles adhering to the furnace wall, the furnace mouth, and the vicinity of the hot water hole before the hot water is discharged, the chromium-containing molten iron can be produced more stably.

The details of the present invention will be described below.
Due to the lack of reports on the liquidus temperature in slag with a high concentration of chromium oxide, the inventors prior to the development of the relationship between basicity and solid phase ratio in slag with a high concentration of chromium oxide on the scale of 30 kg. An diligent investigation was conducted in the melting furnace. In advance, the Al ₂ O ₃ concentration is 5 to 10% by mass, the Cr ₂ O ₃ concentration is 5 to 50% by mass, the MgO concentration is 0 to 10% by mass, and the ratio of CaO to SiO ₂ is 1.0 to 3. A mixture of CaO, SiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ , and MgO reagent was prepared so as to change between 0. Then, each was added into the MgO crucible, and the temperature was raised to 1700 ° C. to dissolve it. Once the melted slag sample is rapidly cooled and crushed, only slag grains with a particle size in the range of 2.0 to 4.0 mm are classified and added onto molten steel heated to 1600 ° C. 30 minutes later. The appearance of the slag was observed. Although the liquid phase ratio varies depending on the composition of the slag, it has been observed that the dissolution rate of slag with a basicity of 1.7 or more and less than 1.9 is extremely slow due to adhesion to the furnace wall and aggregation of slag particles. rice field. In particular, at a high basicity of 1.9 or higher, the formation of MgCr ₂ O ₄ , which is a spinel compound, was suppressed, and the amount of liquid phase formed increased. In addition, the inventors conducted a thermodynamic study of the liquid phase produced in slag having a high chromium oxide concentration. FIG. 2 shows the relationship between the basicity of the slag and the basicity of the liquid phase produced at 1700 ° C. calculated using the thermodynamic calculation software Factsage for each of the chromium oxide concentrations of 20, 30, 40, 50 and 60 mass% in the slag. Is shown in a graph. Here, the basicity in the liquid phase is based on the mass in the liquid phase, and the CaO concentration is divided by the SiO ₂ concentration. The MgO concentration and the _Al2O3 concentration in the slag _were set to 10 mass% and 10 mass%, respectively. The MgO concentration and the _Al2O3 concentration _are the compositions of slag in a general smelting furnace, and the magnitude of these concentrations does not significantly affect the calculation result.

In general, it has been confirmed that the viscosity of slag increases sharply when the basicity of the slag is less than 1.2. Therefore, by keeping the basicity in the liquid phase composition at 1.2 or more, slag adhesion to the furnace wall can be suppressed. In particular, when the basicity of the slag is less than 1.5, a non-uniform state may occur in the slag phase, and the viscosity of the slag may increase locally, which may hinder the operation. ..

Further, when the basicity of the slag exceeds 3.5, hexavalent chromium is generated in the slag, so from the viewpoint of environmental problems, the basicity of the slag needs to be 3.5 or less. Considering the change in the chromium oxide concentration due to the change in operation, it is more desirable that the basicity of the slag is in the range of 2.0 or more and 3.5 or less.

Further, when the concentration of chromium oxide is about 60 mass%, the basicity of the liquid phase portion does not increase so much even if the slag basicity is increased, so it is desirable to set the concentration of chromium oxide in the slag to 50 mass% or less. .. Also, if the chromium oxide concentration in the slag is less than 5 mass%, the demerit of increasing the volume of the slag may outweigh the advantages of chromium that can be recovered by the newly charged carbon or metal source. There is sex. Therefore, it is desirable to secure 5 mass% or more of the chromium oxide concentration in the slag. After supplying oxygen, an appropriate amount of Si-containing raw material or Al-containing raw material is added and weakly reduced to adjust the concentration of chromium oxide within this range. In this case, the slag basicity after acid transfer and after weak reduction changes depending on the addition of the Si-containing raw material, but both the slag basicity after acid transfer and after weak reduction are 1.5 or more and less than 1.7 or It is desirable that the range is 1.9 or more and 3.5 or less.

When the basicity of the slag is adjusted to the range of 1.5 or more and less than 1.7 or 1.9 or more and 3.5 or less, the adhesive force of the slag to the furnace wall is greatly reduced, but it does not mean that the slag does not adhere at all. do not have. However, it is preferable that these adhered slags and the metal particles encapsulated therein, for example, granular iron having a high chromium concentration, are peeled off from the furnace wall by a physical force. At this time, since the oxidizing slag falls on the molten iron having a high oxygen concentration, a large gas generation reaction does not occur. When the attached slag and metal particles are cooled, the force attached to the furnace wall increases, so that the slag and metal particles may be peeled off in a relatively high temperature condition where molten iron is present in the furnace. desirable. To peel off the slag and metal particles from the furnace wall, a heavy machine or the like may be used. By exfoliating the slag and metal particles from the furnace wall before the hot water is discharged, chromium can be reduced and recovered with high efficiency by using a carbon source or a metal source newly added after the hot water is discharged.

If chromium oxide-containing slag remains in the furnace, chromium can be reduced and recovered by adding a new carbon source or metal source to the slag. Examples of the carbon source include hot metal prepared separately, high carbon-containing ferrochrome, and carbonaceous material. Examples of the metal source include ferrosilicon, aluminum pellets, and aluminum dross. Since the reduction reaction of chromium oxide by carbon is an endothermic reaction, oxygen may be supplied or energization may be carried out to supply heat. In the subsequent steps, the composition of the slag may be adjusted again and the hot water may be discharged while the chromium oxide-containing slag remains in the furnace, or the hot water may be discharged after adding a metal reducing agent and draining once. good.

The inventors charged chromium-containing scrap and high-carbon ferrochrome into a 50-ton scale electric furnace, and carried out hot water discharge after electric dissolution and acid transfer decarburization. After the hot water was discharged, ferrochrome and scrap were additionally charged into the furnace and melted by energization again to melt the chromium-containing molten iron. Table 1 shows the experimental conditions. Table 1 shows the C concentration and the Cr concentration as the molten metal composition after acid transfer decarburization. The balance is Fe and unavoidable impurities. In addition, Table 1 shows the slag composition and slag basicity after acid decarburization and before hot water discharge. Processing condition No. In Nos. 1 and 4, as in the conventional case, as a strong reduction, a reducing agent was added in an amount that chemically reduces the total amount of chromium oxide in the slag.

Next, under the experimental conditions shown in Table 1, the conditions of the furnace wall and the hot water outlet were confirmed, and the operational impact was evaluated. The results are shown in Table 2. Here, in the operational stability evaluation, the case where the adhesion to the furnace wall was remarkable and the oxygen gas supply path was obstructed, or the hot water outlet hole was blocked during or before the hot water was discharged and could not be removed was evaluated as x. In addition, the case where the degree of adhesion was mild and could be removed was evaluated as ◯, and the case where the adhesion removal work was within 20 minutes was evaluated as ⊚. In addition, as an evaluation of the amount of reducing material used, when the amount of metal reducing material used, that is, the amount of ferrosilicon or aluminum pellets used was the same as the conventional one, it was evaluated as x, and when it was reduced from the conventional one, it was evaluated as ◯. Furthermore, as the chromium recovery rate, the proportion of chromium recovered in the second step was evaluated. Here, the chromium recovery rate was calculated as (chromium concentration (%) of molten metal x amount of hot water (t) / 100-added chromium amount (t)) / amount of residual chromium in the furnace (t) on a mass basis. .. Further, when the chromium recovery rate was less than 0.3, it was evaluated as x, when it was 0.3 or more and less than 0.5, it was evaluated as 〇, and when it was 0.5 or more, it was evaluated as ⊚. As a comprehensive evaluation, those evaluated as x in any of the operation stability evaluation, the reducing agent usage evaluation and the chromium recovery rate are evaluated as x, and among the rest, the operation stability evaluation and the chromium recovery rate are all evaluated. Those evaluated as ◎ were evaluated as ◎, and other conditions were evaluated as 〇.

Processing condition No. which is an example of the invention. In 6 to 15, stable operation was possible under all conditions, and the amount of reducing agent used could be reduced. Further, the treatment condition No. was adjusted so that the basicity of the slag was in the range of 2.0 to 3.5 and the concentration of chromium oxide in the slag was in the range of 5 mass% or more and 50 mass% or less. In 9, 10, 12 and 15, the work of removing the deposits on the furnace wall was relatively light. Furthermore, using a heavy machine, the slag and metal particles adhering to the furnace wall were pushed in before the hot water was discharged. In 13 to 15, the recovery rate of chromium increased.

In the above example, an example of melting chromium-containing molten iron inexpensively and stably without any influence of operation is shown, but the chromium-containing molten iron produced by the present invention has a high oxygen concentration in the molten iron, so that it is difficult to absorb nitrogen. Therefore, it is also useful as a method for obtaining high-purity molten iron. In addition, the molten iron discharged by this method is discharged with a relatively high sulfur concentration due to the high oxygen concentration in the molten iron, but desulfurization can be performed without problems by performing a reduction treatment in a subsequent process. Is. In addition, since it is not necessary to reduce the oxide in the slag, the amount of the alloy reducing material such as the Si-containing raw material and the Al-containing raw material used is significantly reduced. It is also useful to melt the molten iron having a predetermined component concentration by combining the molten iron discharged by this method and the molten iron melted in another refining container.

The method for producing chromium-containing molten iron of the present invention is industrially useful because it is inexpensive, can suppress slag produced, and can reduce the environmental load.

Claims (3)

In a method for producing chromium-containing molten iron, in which a raw material containing a chromium-containing raw material is melted and crude decarburization is performed by blowing oxygen using an electric furnace for steelmaking.
After adjusting the basicity of the slag to the range of 1.5 or more and less than 1.7 or 1.9 or more and 3.5 or less, the chromium oxide-containing slag produced by blowing oxygen remains in the furnace. The first step of hot water and
It has a second step of reducing the chromium oxide-containing slag remaining by a carbon source or a metal source newly added in the same furnace and recovering the chromium in the molten iron.
Here, the basicity of slag is a method for producing chromium-containing molten iron, characterized in that the CaO concentration is divided by the SiO ₂ concentration based on the mass in the slag. In the first step, the chromium oxide concentration in the slag is set to be in the range of 5 mass% or more and 50 mass% or less by using one or two kinds selected from the Si-containing raw material and the Al-containing raw material after oxygen injection. The method for producing chromium-containing molten iron according to claim 1, wherein the method is adjusted to. The method for producing chromium-containing molten iron according to claim 1 or 2, wherein in the first step, slag and metal particles adhering to the furnace wall are dropped onto the molten iron after oxygen is blown into the furnace wall.

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