WO2021010311A1

WO2021010311A1 - Method for producing low carbon ferrochromium

Info

Publication number: WO2021010311A1
Application number: PCT/JP2020/026995
Authority: WO
Inventors: 博一杉森; 正浩森
Original assignee: Ｊｆｅマテリアル株式会社
Priority date: 2019-07-12
Filing date: 2020-07-10
Publication date: 2021-01-21
Also published as: JPWO2021010311A1; BR112021024006A2; JP7035280B2; JP2022048383A

Abstract

The present invention provides a method for producing low carbon ferrochromium, said method being capable of improving the chromium yield, while being capable of preventing the formation of harmful hexavalent chromium in a slag to be discarded. A method for producing low carbon ferrochromium according to the present invention is provided with: a first step (S1) wherein chromium ore and quick lime are melted in an electric furnace; and a second step (S2) wherein a molten staring material (hereinafter referred to as a primary slag) melted in the first step and a reducing agent are charged into a reaction container, so that low carbon ferrochromium and a secondary slag having a degree of basicity (CaO/SiO₂) adjusted to less than 1.65 are produced. After transferring the secondary slag obtained in the second step (S2) to the electric furnace or the reaction container, a reducing agent is charged thereinto so as to produce a chromium-containing metal and a tertiary slag (S3). The tertiary slag is a harmless slag wherein the chromium oxide content (Cr₂O₃ mass%) is adjusted to 1.4 mass% or less and the degree of basicity (CaO/SiO₂) is adjusted to less than 1.3.

Description

Method for producing low carbon ferrochrome

The present invention relates to a method for producing low carbon ferrochrome.

Low carbon ferrochrome, which is an Fe—Cr alloy having a Cr of 60% by mass or more and a C of 0.1% by mass or less, is generally produced by a method of reducing chromium ore with silicon. The so-called Peran method is adopted as a specific manufacturing method. As shown in FIG. 9, the basic steps of the Peran method are the first step of melting chrome ore and fresh lime in an electric furnace, and the melting raw material (hereinafter referred to as primary slag) melted in the first step in a ladle. It is provided with a second step of producing low-carbon ferrochrome and secondary slag by pouring hot water, charging silicochrome as a reducing agent into the ladle, stirring the mixture, and causing a reduction reaction. The stirring in the second step is usually performed by relaying in which two ladle are prepared and the molten metal of the primary slag containing silicochrome is repeatedly transferred (see Patent Document 1).

Japanese Unexamined Patent Publication No. 1-225743

However, in the conventional method for producing low-carbon ferrochrome, the basicity (CaO / SiO ₂ ) of the secondary slag is increased to about 1.7 to 2.0 in order to increase the chromium yield. This is because the higher the basicity, the more the chromium reduction reaction proceeds, and the lower the chromium content of the secondary slag, that is, the higher the chromium yield. However, if the basicity of the secondary slag (CaO / SiO ₂ ) is increased, there is a problem that hexavalent chromium harmful to the rejected secondary slag is generated.

The present invention has been made in view of the above problems, and a method for producing low carbon ferrochrome which can improve the chromium yield and prevent the formation of hexavalent chromium which is harmful to the rejected slag. The purpose is to provide.

In order to solve the above problems, one aspect of the present invention is a first step of dissolving ferrochrome ore and quicklime in an electric furnace, a melting raw material (hereinafter referred to as primary slag) and a reducing agent dissolved in the first step. Is charged into a reaction vessel to generate a secondary slag having a low carbon ferrochrome and a basicity (CaO / SiO ₂ ) adjusted to less than 1.65, which is a method for producing a low carbon ferrochrome. ..

In a preferred embodiment of the present invention, the secondary slag obtained in the second step is transferred to an electric furnace or a reaction vessel, and then a reducing agent is charged to form a chromium-containing metal and a tertiary slag. The tertiary slag is detoxified by having three steps and having a chromium oxide content (Cr ₂ O ₃ % by mass) of 1.4% by mass or less and a basicity (CaO / SiO ₂ ) of less than 1.3. It is characterized by being a slag.

According to the present invention, by setting the basicity of the secondary slag (CaO / SiO ₂ ) to less than 1.65, the basicity of the tertiary slag (CaO / SiO ₂ ) can be set to less than 1.3. The tertiary slag can be detoxified.

It is a process drawing of the manufacturing method of the low carbon ferrochrome of one Embodiment of this invention. It is a figure which shows the equipment used in the manufacturing method of the low carbon ferrochrome of this embodiment. It is a graph which shows the relationship between the basicity (CaO / SiO ₂ ) of a secondary slag and (Cr) mass% of a secondary slag. It is a vertical sectional view of the reaction vessel used in the 2nd step. It is a graph which shows the relationship between the (Cr) mass% of a tertiary slag and the [Si] mass% of a recovered silicochrome. It is a graph which shows the relationship of the (Cr) mass% of a tertiary slag, the basicity (CaO / SiO ₂ ) of a tertiary slag, and the concentration (mg / l) of Cr ⁶⁺ of a tertiary slag. It is a process drawing of the 3rd step of the manufacturing method of the low carbon ferrochrome of 2nd Embodiment of this invention. It is a process drawing of the 3rd step of the manufacturing method of the low carbon ferrochrome of 3rd Embodiment of this invention. It is a process drawing of the conventional method of manufacturing low carbon ferrochrome.

Hereinafter, a method for producing a low-carbon ferrochrome according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the method for producing a low-carbon ferrochrome of the present invention can be embodied in various forms, and is not limited to the embodiments described in the present specification. The present embodiment is provided with the intention of allowing those skilled in the art to fully understand the invention by adequately disclosing the specification.
(First Embodiment)

FIG. 1 is a process diagram of a method for producing low carbon ferrochrome according to the first embodiment of the present invention. FIG. 2 is a diagram showing equipment used in the method for producing low carbon ferrochrome of the present embodiment.

As shown in FIG. 1, in the method for producing low carbon ferrochrome of the present embodiment, a mixture of chromium ore and quicklime as a medium solvent is dissolved in an electric furnace to produce a dissolved raw material (hereinafter referred to as primary slag). The first step (S1) is provided. As shown in FIG. 2, the chromium ore and quicklime are stored in the hopper 4. As the electric furnace 1, a fixed electric furnace in which a hot water outlet 1a is provided at a position higher than the bottom of the furnace to form a hot water pool is used. The hot water outlet 1a may be provided on the bottom of the furnace. The reason why the hot water pool is formed is that a stable amount of heat is maintained even when the primary slag is discharged. The primary slag is discharged from the hot water outlet 1a into the reaction vessel 2. The hot water temperature of the primary slag is as high as 1400 ° C. or higher and 2000 ° C. or lower.

Next, as shown in FIG. 1, silicochrome, chasing chromium ore, and recovered silicochrome are charged as reducing agents into the reaction vessel 2 in which the primary slag is discharged. Then, the reaction vessel 2 is stirred by bottom-blowing an inert gas to reduce the oxide of chromium ore to generate low-carbon ferrochrome and secondary slag. This reduction step is the second step (S2).

The inert gas is argon or nitrogen. Chasing chrome ore is a cold material (raw material) of chrome ore. Metallic silicon and ferrosilicon can also be used instead of silicochrome. The recovered silicochrome is the silicochrome recovered in the third step described later. As shown in FIG. 2, as the reaction vessel 2, a reaction vessel 2 having a gas bottom blowing device 2a for blowing an inert gas from the furnace bottom is used.

The upper limit of the basicity of the secondary slag in the second step (S2) is adjusted to be less than 1.65, preferably less than 1.5, and more preferably less than 1.4. The lower the lower limit of the basicity of the secondary slag, the more preferable, but in order to secure the reactivity in the third step (S3), the lower limit of the basicity of the secondary slag is set to 1.0 or more.

The reason for adjusting the basicity of the secondary slag to a low level is as follows.
The reduction reaction of chromium oxide of chromium ore with silicon proceeds as follows.
Cr ₂ O ₃ +3 / 2Si → 2Cr + 3/2SiO ₂ … (1)
Here, the liberated SiO ₂ reacts with quicklime as shown in the following equations (2) and (3) to generate secondary slag.
CaO + SiO ₂ → CaO ・ SiO ₂ … (2)
2CaO + SiO ₂ → 2CaO ・ SiO ₂ … (3)
When the secondary slag is generated as in the formulas (2) and (3), the amount of free SiO _{2 in the} formula (1) decreases, and the reduction reaction in the formula (1) proceeds from left to right.

In the conventional method for producing chromium ore, in order to improve the chromium yield, the amount of lime is increased and the basicity of the secondary slag is raised to about 1.7 to 2.0. This is because the higher the basicity, the more secondary slag is generated as in the formulas (2) and (3), and the reduction reaction in the formula (1) proceeds. In addition, there is a standard for low carbon ferrochrome of products having a silicon content of less than 1% by mass, for example. For this reason, it is necessary to weakly reduce the primary slag with silicon so that silicon does not migrate to low-carbon ferrochrome.

However, when the slag has a high basicity, the slag causes a pulverization phenomenon after cooling, and an environmental problem occurs in which harmful hexavalent chromium is eluted from the slag. Therefore, in the present embodiment, the basicity of the secondary slag is adjusted to be low, and the basicity of the tertiary slag is lowered to less than 1.3, preferably less than 1.2, and more preferably less than 1.1. adjust. When the basicity is lowered, CaO is deprived from the hexavalent chromium compound (CaO · CrO ₃ ) that binds to CaO as shown in the following formula (4), and the hexavalent chromium compound (CaO · CrO ₃ ) is replaced with the trivalent chromium compound (CaO · CrO ₃ ). It is considered to be changed to Cr ₂ O ₃ ).
2 (CaO ・ CrO ₃ ) + 2SiO ₂ → 2 (CaO ・ SiO ₂ ) + Cr ₂ O ₃ + 3 / 2O ₂ … (4)

The lower the lower limit of the basicity of the tertiary slag, the more preferable, but in order to reduce the chromium content of the tertiary slag, it is 0.7 or more, preferably 0.8 or more, and more preferably 0.9 or more. To do.

Table 1 shows the relationship between the basicity of the secondary slag (CaO / SiO ₂₎ and the tertiary slag basicity (CaO / SiO _2). When no auxiliary material for adjusting the basicity is added in the third step (S3), there is a positive correlation between the basicity of the secondary slag and the basicity of the tertiary slag. As shown in Table 1, if the basicity of the secondary slag is less than 1.65, the basicity of the tertiary slag can be reduced to less than 1.3. On the other hand, if the basicity of the secondary slag is larger than 1.65, the basicity of the tertiary slag exceeds 1.3.

In the present embodiment, the reaction vessel 2 having a gas bottom blowing device having a high stirring ability is used to improve the thermal efficiency and the reactivity of the reduction reaction. Therefore, even if the basicity is lowered to less than 1.65, it is possible to prevent the chromium yield from being lowered. When quicklime is reduced and the basicity is lowered, the activity coefficient of SiO ₂ is increased, the reduction reaction of chromium in the formula (1) is less likely to occur, and the (Cr) mass% of the secondary slag is increased. However, as shown in FIG. 3, since the reduction reaction proceeds by the gas bubbling of the gas bottom blowing device, the (Cr) mass% of the secondary slag can be reduced. By reducing the (Cr) mass% of the secondary slag, advantageous operation can be performed.

FIG. 4 is a vertical cross-sectional view of the reaction vessel 2 having the gas bottom blowing device 2a. As shown in FIG. 4,

refractories

8 and 9 are applied to the bottom 6a of the iron skin 6 of the reaction vessel 2. A plug 19 of the gas bottom blowing device 2a is arranged at the center of the bottom of the reaction vessel 2. When an inert gas is introduced into the pipe portion 17 of the plug 19, the inert gas is blown into the reaction vessel 2 from the plug 19, and the molten metal in the reaction vessel 2 is agitated, that is, gas bubbling.

In the operation of the second step (S2), the reaction of the formula (1) proceeds from the primary slag as described above. At the initial stage of operation, the reaction vessel 2 is mainly composed of primary slag. As the reaction progresses, a molten ferrochrome (metal 21) is formed, and the secondary slag 22 is present on the molten ferrochrome (metal 21). Finally, the volume ratio of the secondary slag 22: metal 21 is approximately 4: 1. In order to increase the reactivity in the presence of a large amount of highly viscous secondary slag 22, it is necessary to increase the stirring capacity, and for this purpose, the gas bottom blowing device that blows the inert gas into the bottom of the reaction vessel 2. 2a is used.

Generally, when molten metal is the main component, in order to increase the stirring capacity, it is preferable to arrange the plug 19 of the gas bottom blowing device 2a at a position offset from the center of the bottom of the reaction vessel 2 (eccentric position). It is known (see, for example, Japanese Patent Application Laid-Open No. 1-177333). However, when a large amount of highly viscous secondary slag 22 is present as in the present embodiment, when the plug 19 of the gas bottom blowing device 2a is arranged at the eccentric position of the bottom of the reaction vessel 2, the side on which the plug 19 is arranged is arranged. The opposite side becomes a weakly agitated state, and undissolved chamium ore remains on the opposite side. On the other hand, as in the present embodiment, by arranging the plug 19 of the gas bottom blowing device 2a in the central portion of the bottom of the reaction vessel 2, the plug 19 rises from the central portion of the bottom in the reaction vessel 2 and then radially. A flow of molten metal is formed toward the surrounding area. Therefore, the inside of the reaction vessel 2 can be uniformly agitated, and the chasing chromium ore can be involved and dissolved. A plurality of plugs may be arranged on a circle centered on the central portion of the bottom of the reaction vessel 2. Even in this way, the inside of the reaction vessel 2 can be uniformly stirred.

Although the chromium yield is reduced, as the reaction vessel 2 in the second step, a top-blown reaction vessel in which an inert gas is blown by a lance may be used, or two pans are used and two pans are used. Relaying may be performed between the pots.

In the second step, siliconochrome is used as the reducing agent, but a silicon-based reducing agent such as metallic silicon may be used in addition to silicochrome. Further, in addition to the silicon-based reducing agent, an aluminum-based reducing agent such as aluminum or an aluminum alloy, a magnesium-based reducing agent such as magnesium or a magnesium alloy, or a calcium-based reducing agent such as calcium or a calcium alloy may be used. Further, a mixture of these reducing agents may be used.

As shown in FIG. 1, the molten metal of low carbon ferrochrome produced by the reduction reaction is cast into a mold to become a product. The low carbon ferrochrome of the product contains 60% by mass or more of Cr, 1.0% by mass or less of Si, and 0.1% by mass or less of C. On the other hand, the secondary slag produced by the reduction reaction is separated from the molten metal of low carbon ferrochrome and then charged into the electric furnace 3 (see FIG. 2) or the reaction vessel.

Next, as shown in FIG. 1, ferrosilicon as a reducing agent is charged into the electric furnace 3 or the reaction vessel in which the secondary slag is charged, and is reacted with the chromium oxide remaining in the secondary slag. To generate recovered silicon chrome and tertiary slag. This reduction step is the third step (S3).

Here, a large amount of ferrosilicon as a reducing agent, that is, 1 time or more, preferably 2 times or more the reduction equivalent of chromium oxide, is charged to make a strong reduction, and the chromium oxide content of the tertiary slag is increased by 1.4 mass. % Or less, preferably 1.0% by mass or less. This is to reduce the hexavalent chromium of the tertiary slag and to improve the chromium yield. The Si content of the recovered silicochrome is 20% by mass or more and 70% by mass or less. When the Si content of the recovered silicochrome is less than 20% by mass, the chromium oxide content of the tertiary slag becomes high. Even if the Si content of the recovered silicochrome exceeds 70% by mass, the effect of reducing the chromium oxide of the tertiary slag is small.

FIG. 5 is a graph showing the relationship between the chromium content of the tertiary slag ((Cr) mass%) and the Si content of the recovered silicochrome ([Si] mass%). As shown in FIG. 5, if the silicon content of the recovered silicon chrome is 30% by mass or more (that is, if the secondary slag is strongly reduced), the chromium content of the tertiary slag is 1.0% by mass or less. Can be done. Even if the silicon content of the recovered silicon chrome exceeds 60% by mass, the effect of reducing the chromium content of the tertiary slag is small.

The third step is performed while ensuring the temperature of the molten metal of the recovered silicochrome and the tertiary slag to be 1250 ° C. or higher. If the temperature of the molten metal is below 1250 ° C., the third step is carried out in an electric furnace 3 or a reaction vessel equipped with heating means.

The basicity of the tertiary slag is as low as less than 1.3. The reason for lowering the basicity is to prevent the formation of hexavalent chromium, which is harmful to the tertiary slag, as described above. Silica stone (SiO ₂ ) as an auxiliary raw material may be added to the electric furnace 3 or the reaction vessel as necessary in order to adjust the basicity to a low level. Tertiary slag is detoxified slag, used for roadbed materials or fertilizers, or landfilled in factories. The amount (concentration) of hexavalent chromium eluted from the tertiary slag is 0.05 mg / l or less.

The recovered siliconochrome is charged into the reaction vessel 2 together with the silicochrome. Since part of the silicochrome is replaced by the recovered silicochrome, the silicochrome is reduced. The recovered silicon chrome may be charged into the electric furnace 3 or the reaction vessel of the third step (S3) and used as a partial substitute for ferrosilicon.

In the third step, the electric furnace 3 or the reaction vessel may be used. If the electric furnace 3 is used in the third step (S3), the reactivity of the reduction reaction can be improved, so that even if the basicity of the tertiary slag is lowered to less than 1.3, the chromium yield is lowered. Can be prevented. The electric furnace 3 may be provided with a gas bottom blowing device. The reaction vessel may be a reaction vessel having a gas bottom blowing device, or a top-blowing type reaction vessel in which an inert gas is blown from a lance. The gas bottom blowing device provided in the electric furnace 3 or the reaction vessel is arranged in the central portion of the bottom of the electric furnace 3 or the reaction vessel, similarly to the gas bottom blowing device 2a of the reaction vessel 2 in the second step described above. Is desirable. The volume ratio of slag to metal in the second step is about 4: 1, while the volume ratio of slag to metal in the third step is about 10: 1. In order to increase the stirring power of the molten metal in the third step, the amount of stirring gas (l / min) per ton of the molten metal in the third step is made larger than the amount of stirring gas (l / min) per ton of the molten metal in the second step. Is desirable.

For example, solidified slag that has been landfilled in a factory or temporarily placed in a factory and solidified may be added to the secondary slag. The solidified slag is a secondary slag produced by the operation of the previous method for producing low carbon ferrochrome (secondary slag produced by relaying using two conventional ladle and / or the reaction vessel of the present embodiment). Secondary slag produced by gas bubbling with 2) contains solidified slag and contains chromium oxide. The chromium oxide content of the solidified slag may be 1.4% by mass or more. When the solidified slag is added to the secondary slag, the third step is performed in an electric furnace 3 or a reaction vessel equipped with a heating means to keep the molten metal of the secondary slag warm and redissolve the solidified slag. The solidified slag may be added to the electric furnace 1 that produces the primary slag.

In the above embodiment, ferrosilicon is used as the reducing agent in the third step, but a silicon-based reducing agent such as metallic silicon may be used in addition to ferrosilicon. Further, in addition to the silicon-based reducing agent, an aluminum-based reducing agent such as aluminum or an aluminum alloy, a magnesium-based reducing agent such as magnesium or a magnesium alloy, or a calcium-based reducing agent such as calcium or a calcium alloy may be used. Further, a mixture of these reducing agents may be used.

A method for quantifying the chromium oxide content of slag and a method for quantifying the basicity of slag will be described. The chromium oxide content of slag is obtained by converting the Cr content of slag into an oxide. Specifically, the total amount of chromium oxide is Cr ₂ O ₃ , and the chromium oxide content = Cr content × 152/104. To reduce the chromium oxide content of the tertiary slag to 1.4% by mass or less as in the present embodiment, the chromium content of the tertiary slag is 1.4 × 104/152 = 0.96 ≈ 1% by mass or less. Means to. The chromium content of the slag is represented by ((Cr) mass%). The chromium oxide content of slag is represented by (Cr ₂ O ₃ % by mass). An ICP (Inductively Coupled Plasma) emission spectroscopic analysis method is used as a method for quantifying Cr of slag. In this analysis method, "JIS G1313-1 2012 decomposition by alkaline melting" is used for the decomposition of the sample.

The basicity of slag (CaO / SiO ₂ ) is expressed by the CaO content of slag / SiO ₂ content of slag. The CaO content of the slag is obtained by converting the Ca content of the slag into an oxide, and CaO content = Ca content × 56/40. The SiO ₂ content of the slag is obtained by converting the Si content of the slag into an oxide, and SiO ₂ content = Si content × 60/28. An ICP (Inductively Coupled Plasma) emission spectroscopic analysis method is used as a method for quantifying Ca and Si of slag. In this analysis method, "JIS G1313-1 2012 decomposition by alkaline melting" is used for the decomposition of the sample.

FIG. 6 shows the relationship between the chromium content of the tertiary slag ((Cr) mass%), the basicity of the tertiary slag (CaO / SiO ₂ ), and the concentration of hexavalent chromium of the tertiary slag (mg / l). It is a graph.

As shown in FIG. 6, the chromium content ((Cr) mass%) of the tertiary slag is 1 mass% or less, that is, the chromium oxide content (Cr ₂ O ₃ mass%) is 1.4 mass% or less, and the base is used. By adjusting the degree (CaO / SiO ₂ ) to 0.9 to 1.3, the concentration of hexavalent chromium in the tertiary slag can be reduced to 0.04 (mg / l) or less. This value satisfies the environmental standard of 0.05 (mg / l) or less specified in Notification No. 46 of the Environment Agency.

On the other hand, when the basicity (CaO / SiO ₂ ) is 1.4 to 1.6, the chromium content of the slag is required to reduce the concentration of hexavalent chromium to 0.04 (mg / l) or less. ((Cr) mass%) must be maintained below 0.3, and stable operation cannot be performed. Further, when the basicity (CaO / SiO ₂ ) is 1.7 or more, the tertiary slag collapses after cooling.

For the analysis and measurement of the concentration of hexavalent chromium (mg / l), the dissolution test of hexavalent chromium of Notification No. 46 of the Environment Agency in August 1991 is used. The Environmental Agency Notification No. 46 states that the concentration of hexavalent chromium is 0.05 (mg / mg / mg) as a standard that should be maintained in order to protect human health and protect the living environment (“environmental standard”). l) It is stipulated that the following is true. Table 2 shows the test method of the dissolution test specified in Notification No. 46 of the Environment Agency.

The method for producing low-carbon ferrochrome of the present embodiment has been described above. According to the method for producing low-carbon ferrochrome of the present embodiment, the following effects are obtained.

By setting the basicity of the secondary slag to less than 1.65, the basicity of the tertiary slag can be reduced to less than 1.3, and the tertiary slag can be detoxified.

In the second step (S2), since the reaction vessel 2 having the gas bottom blowing device 2a having high thermal efficiency and stirring ability is used, the reactivity of the reduction reaction can be improved. Therefore, the basicity can be lowered to less than 1.65 without lowering the chromium yield, and the operation with a reduced amount of lime can be performed. Further, since the reaction vessel 2 having the gas bottom blowing device 2a is used, the amount of additional chrome ore can be increased and the electric power intensity can be reduced. The electric power intensity is the amount of electric power used per product t, and specifically (primary slag dissolved electric energy / product production amount).

In the third step (S3), since silica stone as an auxiliary raw material is charged into the electric furnace 3 or the reaction vessel, the basicity of the tertiary slag can be easily adjusted to less than 1.3.

Since the solidified slag is added to the secondary slag in the third step (S3), for example, the solidified slag landfilled or temporarily placed in the factory can be detoxified.

In the third step (S3), the solidified slag is dissolved and the dissolved solidified slag is reduced in an electric furnace, so that the reactivity of the reduction reaction can be improved.

In the third step (S3), the chromium-containing metal (recovered silicochrome) is recovered from the secondary slag, so that the chromium yield can be improved.

It is preferable to use argon as the inert gas. By using argon, the stirring power can be increased and nitrogen can be prevented from being mixed into the low carbon ferrochrome of the product.

When producing low carbon ferrochrome (Cr is 60% by mass or more, Si is 1.0% by mass or less, C is 0.1% by mass or less), the chromium yield can be improved to 95% or more.

Since the electric furnace in the first step (S1) is the fixed electric furnace 1, the solubility of the primary slag can be improved. In addition, since continuous energization is possible without stopping the power when hot water is discharged, the operating rate can be improved.

Since the hot water temperature of the primary slag in the first step (S1) is as high as 1400 ° C. or higher and 2000 ° C. or lower, the reactivity of the reduction reaction in the second step (S2) can be improved.

Since the chromium oxide content of the tertiary slag is 1.0% by mass or less and the basicity of the tertiary slag is 0.9 or more and less than 1.1, hexavalent chromium harmful to the tertiary slag is generated. Can be prevented more.
(Second Embodiment)

FIG. 7 is a process chart of the third step of the method for producing low carbon ferrochrome according to the second embodiment of the present invention. Since the first step and the second step are the same as the method for producing low carbon ferrochrome of the first embodiment, the description thereof will be omitted.

The electric furnace is charged with solidified slag, reducing agent, and auxiliary raw materials. The solidified slag is as described above. The reducing agent is a silicon-based reducing agent, an aluminum-based reducing agent, a magnesium-based reducing agent, a calcium-based reducing agent, or a mixture of these reducing agents. The reducing agent is added at least once, preferably at least twice the reduction equivalent of the chromium oxide and iron oxide of the solidified slag. Auxiliary raw materials are silica stone, quicklime, etc., and are used to adjust the basicity of tertiary slag.

In the electric furnace, the solidified slag, the reducing agent, and the auxiliary raw material are melted, and the melted solidified slag is reduced by the reducing agent to generate a chromium-containing metal and a tertiary slag (S31). The chromium oxide content of the tertiary slag is adjusted to 1.4% by mass or less, and the basicity is adjusted to less than 1.3.

By adjusting the chromium oxide content of the tertiary slag to 1.4% by mass or less and the basicity of the tertiary slag to less than 1.3, the hexavalent value of the tertiary slag is similar to that of S3 of the first embodiment. The chromium concentration can be reduced to 0.04 (mg / l) or less. Therefore, harmful solidified slag that has been landfilled or temporarily placed in the factory can be converted into harmless tertiary slag. In addition, the produced chromium-containing metal can be reused as a reducing agent.

As shown by the alternate long and short dash line in FIG. 7, the secondary slag produced in the second step may be charged into the electric furnace. Further, the electric furnace may be provided with a gas bottom blowing device.

According to the method for producing low-carbon ferrochrome of the second embodiment, the same effect as that of the method for producing low-carbon ferrochrome of the first embodiment is obtained.
(Third Embodiment)

FIG. 8 is a process chart of the third step of the method for producing low carbon ferrochrome according to the third embodiment of the present invention. Since the first step and the second step are the same as the method for producing low carbon ferrochrome of the first embodiment, the description thereof will be omitted.

In the third step of the method for producing low-carbon ferrochrome of the second embodiment, the solidified slag is dissolved and the dissolved slag is reduced in an electric furnace (S31). On the other hand, in the third step of the method for producing low carbon ferrochrome of the third embodiment, the solidified slag is melted in an electric furnace (S301), and the melted solidified slag is reduced in a reaction vessel (S302). ).

The electric furnace is charged with auxiliary raw materials such as silica stone and quicklime for adjusting the basicity of solidified slag and tertiary slag. The electric furnace melts the solidified slag and the auxiliary raw material (S301). The melted solidified slag and auxiliary raw materials are discharged from the electric furnace to the reaction vessel. As the reaction vessel, two ladle for relaying may be used, a reaction vessel having a gas bottom blowing device may be used, or a top-blowing type reaction vessel may be used.

In the reaction vessel, the dissolved solidified slag is reduced with a reducing agent to produce a chromium-containing metal and a tertiary slag (S302). The chromium oxide content of the tertiary slag is adjusted to 1.4% by mass or less, and the basicity is adjusted to less than 1.3.

Note that, as shown by the alternate long and short dash line in FIG. 8, the secondary slag produced in the second step may be charged into the electric furnace. Further, after melting and reducing the slag containing the solidified slag in an electric furnace, the finishing reduction of the melted slag may be carried out in a ladle as a reaction vessel. Further, the electric furnace may be provided with a gas bottom blowing device.

According to the method for producing low-carbon ferrochrome of the third embodiment, the same effect as that of the method for producing low-carbon ferrochrome of the first embodiment is obtained.
(Example 1)

Low carbon ferrochrome was produced according to the production process diagram of FIG. Table 3 shows the composition of the chromium ore as the raw material used in this example.

1750 kg of chrome ore and 830 kg of quicklime were charged into the fixed electric furnace 1 and melted to melt the primary slag. The primary slag was discharged into the reaction vessel 2, and 310 kg of silicochrome and 260 kg of recovered silicochrome were charged therein. Next, argon gas was bottom-blown into the reaction vessel 2 and stirred. Then, the produced secondary slag was separated, and the obtained molten metal of 1000 kg of low-carbon ferrochrome was cast into a mold to obtain a product. Table 4 shows the composition of the product low carbon ferrochrome. Table 5 shows the composition of the secondary slag. The basicity of the secondary slag was 1.32. The method for quantifying each component of ferrochrome is standardized in "JIS G1301-1 to 5 2012".

On the other hand, the separated secondary slag was received in a reaction vessel, 230 kg of ferrosilicon was charged, and argon gas was bottom-blown into the reaction vessel to stir. Then, the produced tertiary slag and recovered silicochrome were separated to obtain 1930 kg of tertiary slag and 260 kg of recovered silicochrome. This recovered silicochrome was charged into the primary slag together with the silicochrome. Table 6 shows the composition of the tertiary slag. Table 7 shows the composition of the recovered silicochrome.

As shown in Table 6, the basicity of the tertiary slag was 37.0 / 36.5 ≈ 1.01. The tertiary slag did not spontaneously decay after cooling, and no elution of hexavalent chromium was confirmed. As shown in Table 8, the yield of chromium was as high as 97% or more.

(Example 2)

Similar to Example 1, low carbon ferrochrome and secondary slag were produced according to the manufacturing process diagram of FIG. Table 9 shows the composition of the secondary slag of Example 2. The basicity of the secondary slag was 1.63.

Similar to Example 1, recovered silicochrome and tertiary slag were produced from the secondary slag according to the manufacturing process diagram of FIG. Table 10 shows the composition of the tertiary slag of Example 2. The basicity of the tertiary slag was 1.29. The tertiary slag did not spontaneously decay after cooling, and no elution of hexavalent chromium was confirmed.

(Example 3)

In the same manner as in Example 1, secondary slag and tertiary slag were produced according to the manufacturing process diagram of FIG. Table 11 shows the basicity (CaO / SiO ₂ ), chromium oxide content (Cr ₂ O ₃ % by mass), and Cr yield (%) of the secondary slags and tertiary slags of operations 1 to 4 satisfying the scope of the present invention. ), Hexavalent chromium elution amount (concentration (mg / l)) is shown. Hexavalent chromium was not detected in operations 1 to 3, and it was the detection limit of hexavalent chromium in operations 4. In Operation 4, the reactivity decreased and the chromium yield decreased to 95%, but in Operations 1 to 4, the chromium yield was 95.0% or more.

(Conventional example)

Low carbon ferrochrome was produced according to the production process diagram of FIG. In the manufacturing process of this low-carbon ferrochrome, the reduction operation of the primary slag is performed by relaying, and the recovery silicochrome is recovered from the secondary slag and the operation of adding the recovered silicochrome to the primary slag is not performed. Different from the example. Table 12 shows the composition of the chromium ore which is the raw material used in the conventional example.

1740 kg of chrome ore and 1060 kg of quicklime were charged into an electric furnace and melted to melt the primary slag. The primary slag was taken into a ladle and 600 kg of silicochrome was charged therein. Then, the mixture was stirred by relaying. Then, 2200 kg of the produced secondary slag was separated, and 1000 kg of the obtained molten metal of low carbon ferrochrome was cast into a mold to obtain a product. Table 13 shows the composition of the product low carbon ferrochrome, and Table 14 shows the composition of the secondary slag.

As shown in Table 14, in the conventional example, the chromium oxide content of the secondary slag was as high as 6.4%, and the basicity was also as high as 1.70. As shown in Table 15, the yield of chromium was as low as 85%. Harmful hexavalent chromium was generated during the secondary slag.

This specification is based on Japanese Patent Application No. 2019-130324 filed on July 12, 2019. All this content is included here.

S1 ... 1st process S2 ... 2nd process S3 ... 3rd process 1 ... Electric furnace (fixed electric furnace)
2 ... Reaction vessel 3 ... Electric furnace

Claims

The first step of melting chrome ore and quicklime in an electric furnace,
The dissolved raw material (hereinafter referred to as primary slag) dissolved in the first step and the reducing agent were charged into the reaction vessel, and the low carbon ferrochrome and basicity (CaO / SiO 2 ) were adjusted to less than 1.65. A method for producing low carbon ferrochrome, comprising a second step of producing the next slag.
After transferring the secondary slag obtained in the second step to an electric furnace or a reaction vessel, a third step of charging a reducing agent to generate a chromium-containing metal and a tertiary slag is provided.
The tertiary slag is a detoxified slag in which the chromium oxide content (Cr 2 O 3 % by mass) is adjusted to 1.4% by mass or less and the basicity (CaO / SiO 2 ) is adjusted to less than 1.3. The method for producing low carbon ferrochrome according to claim 1.
The second step is characterized in that the primary slag and the reducing agent are charged into the reaction vessel having a gas bottom blowing device, and an inert gas is blown from the furnace bottom of the reaction vessel to stir. The method for producing a low carbon ferrochrome according to claim 1 or 2.
The reducing agent charged in the second step is a silicon-based, aluminum-based, magnesium-based, or calcium-based reducing agent, or a mixture thereof.
The low-carbon ferrochrome according to claim 2, wherein the reducing agent charged in the third step is a silicon-based, aluminum-based, magnesium-based, or calcium-based reducing agent, or a mixture thereof. Production method.
The low-carbon ferrochrome according to claim 2 or 4, wherein in the third step, an auxiliary material for adjusting the basicity (CaO / SiO 2 ) of the tertiary slag is added to the secondary slag. Manufacturing method.
The method for producing a low-carbon ferrochrome according to claim 2, 4 or 5, wherein in the third step, solidified slag is added to the secondary slag.
The method for producing low-carbon ferrochrome according to claim 6, wherein in the third step, the secondary slag containing the solidified slag is dissolved and reduced in the electric furnace.
The low carbon according to claim 6, wherein in the third step, the secondary slag containing the solidified slag is melted in the electric furnace, and the dissolved secondary slag is reduced in the reaction vessel. How to make ferrochrome.
Claims 2, 4, 5, 6, 7 characterized in that the chromium-containing metal obtained in the third step is reused as at least a part of the reducing agent in the second step and / or the third step. , Or the method for producing low carbon ferrochrome according to 8.
The method for producing low-carbon ferrochrome according to claim 3, wherein the inert gas is argon or nitrogen.
The low-carbon ferrochrome produced in the second step contains 60% by mass or more of Cr, 1.0% by mass or less of Si, and 0.1% by mass or less of C.
The method for producing a low-carbon ferrochrome according to claim 2, 4, 5, 6, 7, 8 or 9, wherein the yield of Cr is 95% or more.
The tertiary slag is a detoxified slag in which the chromium oxide content (Cr 2 O 3 % by mass) is adjusted to 1.0% by mass or less and the basicity (CaO / SiO 2 ) is adjusted to less than 1.2. The method for producing low carbon ferrochrome according to claim 2, 4, 5, 6, 7, 8, 9, or 11.
The method for producing low-carbon ferrochrome according to any one of claims 1 to 12, wherein the electric furnace in the first step is a fixed electric furnace.
The method for producing low-carbon ferrochrome according to any one of claims 1 to 13, wherein the hot water temperature of the primary slag in the first step is 1400 ° C. or higher and 2000 ° C. or lower.
The method for producing a low-carbon ferrochrome according to any one of claims 1 to 14, wherein the basicity (CaO / SiO 2 ) of the secondary slag is adjusted to less than 1.5.