JP6230531B2 - Method for producing metallic chromium - Google Patents

Description

  The present invention relates to a method for producing metallic chromium used for corrosion-resistant and heat-resistant materials (superalloy), electronic materials and the like (for example, magnetic materials and semiconductor materials).

As a typical method for producing metal chromium, the applicant has proposed a method for producing metal chromium in which chromium oxide is reduced by silicon (see Patent Document 1). In this silicon reduction method, first, chromium oxide, metallic silicon, and lime are charged into an electric furnace as raw materials. Metallic silicon is used as a reducing agent. Next, the electric furnace is energized to melt these raw materials. The dissolved metal silicon and chromium oxide react, and chromium oxide is reduced by silicon. Silicon oxide (SiO ₂ ) generated by the reduction reaction reacts with lime (CaO) to form slag.

Japanese Patent No. 3338701

  In recent years, iron contained as impurities and metallic chromium with a low P content have been demanded. In said silicon reduction method, since iron is contained in the metallic silicon used as a reducing agent, there exists a subject that it is difficult to make low iron content of metallic chromium.

Indeed, if a high purity metal having a low iron content is used for the metal silicon, the iron content attributable to the metal silicon can be reduced. However, in the silicon reduction method, it is necessary to increase the basicity (CaO / SiO ₂ ) in order to advance the reduction reaction, and for that purpose, a large amount of lime is used. Since this large amount of lime also contains iron, there is a problem that there is a limit in reducing the iron content of metallic chromium.

  By the way, if aluminum is used instead of metallic silicon as the reducing agent, the content of iron contained in the reducing agent can be reduced. For this reason, it is conceivable to adopt an aluminum thermite method in which chromium oxide is reduced by aluminum.

In the aluminum thermite method, first, acicular aluminum (Al) as a reducing agent is mixed with chromium oxide (Cr ₂ O ₃ ), and the mixture is charged into a reaction furnace. Next, magnesium powder is placed on the mixture and ignited. Heat is propagated through the mixture to initiate the reaction between chromium oxide and aluminum. Aluminum generates high temperatures while reducing chromium oxide. This high heat causes metal chromium metal to settle to the bottom of the reactor. Slag with a lighter specific gravity than metal is separated from the metal. The reduction reaction of the aluminum thermit method continues for 10 to 15 minutes. After the molten metal and slag are solidified, the molten metal and slag are taken out from the reaction furnace, and the metal is pulverized to obtain metal chromium.

  However, in the above aluminum thermite method, there is a problem that expensive acicular aluminum is required for the reducing agent or the reaction is stopped when the reaction heat of aluminum is reduced, so that the yield of chromium is lowered. And since the aluminum used as a reducing agent transfers to metal chromium, there exists a subject that the content of aluminum of metal chromium cannot be made low.

  Then, this invention aims at providing the manufacturing method of the metal chromium which can also raise the yield of chromium collection | recovery and can also reduce the iron content and P content of the metal chromium manufactured as a product. To do.

  In order to solve the above problems, one embodiment of the present invention includes a step of charging chromium oxide, aluminum, and lime as raw materials into an electric furnace, and the electric furnace is energized to dissolve the raw materials, Reducing with aluminum to produce a primary metal containing chromium and primary slag; extracting the primary slag from the electric furnace; adding basic flux to the primary metal of the electric furnace; A method of producing metallic chromium, comprising: energizing the electric furnace to dissolve the basic flux and oxidizing and removing aluminum remaining in the primary metal to generate a secondary metal.

  According to the present invention, the heat for melting the raw material is guaranteed by the electric furnace, so that the reduction reaction of chromium oxide can be maintained for a long time, and the reduction reaction can be advanced with a high yield. Moreover, since aluminum is used as the reducing agent, the iron and P contents contained in the reducing agent can be reduced. Furthermore, when aluminum is used as the reducing agent, aluminum remains in the primary metal, but the primary metal aluminum can be removed by oxidizing and refining the primary metal. Therefore, the iron content and aluminum content of the metal chromium recovered as a product can be reduced.

The flowchart of the manufacturing method of the metal chromium of one Embodiment of this invention Graph showing the relationship between the aluminum content in the primary metal and the Cr content in the primary slag

  Hereinafter, the manufacturing method of the metal chromium of one Embodiment of this invention is demonstrated based on an accompanying drawing. FIG. 1 shows a flowchart of a method for producing metallic chromium of the present embodiment.

In the method for producing metallic chromium of the present embodiment, first, chromium oxide (Cr ₂ O ₃ ) as a raw material, aluminum (Al) as a reducing agent, and lime (CaO) are charged into an electric furnace (S1). One of the features of the method for producing metallic chromium according to the present embodiment is that an electric furnace is used in spite of the aluminum reduction method in which chromium oxide is reduced by aluminum.

  As the electric furnace, an arc melting furnace is used in which an arc discharge is generated using a graphite electrode and a raw material is melted using a large amount of heat generated at that time. The power source for generating the arc may be direct current or alternating current. An arc melting furnace that can be tilted to discharge the generated molten metal and discharge the slag is used.

Chromium oxide is a product obtained by chemically treating chromium ore and / or chromium ore. Lime is used as a flux that promotes the melting of chromium ore. If there is no flux on the metal, a stable arc cannot be generated in the arc melting furnace. The amount of lime is less than the amount of lime used in the silicon reduction process. This is because, in the silicon reduction method, the reduction efficiency of chromium oxide increases as the basicity (CaO / SiO ₂ ) increases, so that the amount of lime used increases. This is because the chromium metal production method of the present embodiment reduces chromium oxide with aluminum, and the reduction efficiency of chromium oxide is independent of basicity.

  Aluminum is used as a reducing agent. Only aluminum is used as the reducing agent, and silicon is not used. As the aluminum, bulk metallic aluminum such as 40 g, 10 g, 1 g, or the like is used. Since the heat for melting the aluminum is guaranteed by the electric furnace, it is not necessary to use acicular aluminum as used in the aluminum thermite method. Since aluminum has a low specific gravity, it floats when dissolved, and the reduction reaction may not proceed. For this reason, when charging a raw material in an arc melting furnace, chromium oxide, aluminum, and lime are mixed.

After charging the raw materials, the arc melting furnace is energized to perform a reduction process (S1). When the raw material is melted, the molten aluminum and chromium oxide react as shown in the following reaction formula, and reduction with aluminum proceeds while producing Al ₂ O ₃ . The primary metal containing chromium is generated arc melting furnace, the primary slag and the Al ₂ O ₃ was produced by the reduction reaction of CaO reacts is formed.

(Chemical formula 1)
Cr ₂ O ₃ + 2Al → 2Cr + Al ₂ O ₃ (1)
CaO + Al ₂ O ₃ → CaO · Al ₂ O ₃ (2)

  In the reduction process, the chromium content of the primary metal is 95% or more. However, the aluminum content, silicon content, and iron content are not reduced to the target levels (for example, the aluminum content is 0.02% by mass or less and the silicon content is 0.05% by mass or less). For this reason, a refining process is required. The refining process will be described later.

The chromium content of the primary slag is 1% or less. In order to make the chromium content in the primary slag 1 mass% or less, the aluminum content in the primary metal is set to about 0.2 to 3 mass%. The main component of primary slag is calcium aluminate containing CaO and Al ₂ O ₃ as main components. This calcium aluminate is used as a desulfurizing agent for steel making.

  FIG. 2 shows the relationship between the aluminum content in the primary metal and the Cr content in the primary slag. When the aluminum content in the primary metal is 0.2% by mass or more, the Cr content in the primary slag is reduced to 1.0% by mass. For this reason, the yield of chromium can be set to a high value of 90% or more.

  Next, the arc melting furnace is tilted to discharge the primary slag (S2 in FIG. 1). Next, the basic flux is charged into the arc melting furnace, and the arc melting furnace is energized again to melt the basic flux (S3). The basic flux is lime (CaO) or magnesia (MgO). In this embodiment, lime (CaO) is used.

  When the basic flux is melted, primary metal dealumination, silicon removal, and sulfur removal proceed to form secondary slag. That is, the primary metals aluminum, silicon, and sulfur are oxidized and removed from the primary metal. Since aluminum, silicon, and sulfur are highly oxidizable, they react with oxygen in the air through the secondary slag and oxidize. Since the secondary slag is thin, aluminum, silicon, and sulfur are easily oxidized. Volatile desulfurization of sulfur is also performed at high temperatures.

  By this oxidative refining, a secondary metal is obtained (S4). The aluminum content in the secondary metal is 0.02 mass% or less, the silicon content is 0.05 mass% or less, the sulfur content is 0.001 mass% or less, the iron content is 0.20 mass% or less, phosphorus Content is 0.003 mass% or less. The aluminum content in the primary metal is reduced from about 0.2 to 3% by mass to 0.02% by mass or less. Moreover, since silicon is not used as the reducing agent, the silicon content in the primary metal is about 0.3% by mass. By oxidative refining, the silicon content in the primary metal is reduced to 0.05 mass% or less. In addition, the sulfur content becomes extremely low at 0.001% by mass or less by high temperature refining and high basicity operation. Chrome yield is over 94%.

  When the dealumination of the primary metal, desiliconization, desulfurization, etc. is completed, the energization is stopped and the secondary metal and secondary slag are poured out into the pan. Secondary metal and secondary slag are cast from the ladle into a mold.

  After casting, the cooled secondary metal ingot is taken out of the mold and crushed into briquettes (S5, S6). The metallic chromium thus obtained is of high purity but has a slightly high oxygen content and nitrogen content. Therefore, these gas components are removed by vacuum heat treatment in a vacuum processing facility (S7).

Thus, metallic chromium having a chromium content of 99.0% or more is produced (S8). The content of impurity elements (aluminum, iron, silicon, sulfur, phosphorus, oxygen, nitrogen) in metallic chromium is extremely low. Iron and phosphorus contained in metallic chromium are derived from the introduction of raw materials. By using aluminum as the reducing agent, the amount of iron derived from the reducing agent can be reduced as compared with the case of using metal silicon as the reducing agent. Moreover, since the quantity of lime used in the reduction | restoration process of chromium oxide can also be decreased, content of iron and phosphorus derived from lime can be reduced. That is, in the silicon reduction method, it is necessary to increase the basicity of slag (CaO / SiO ₂ ) and to increase the amount of lime inevitably in advance of the reduction reaction of chromium oxide. On the other hand, in the method for producing metallic chromium of the present embodiment, CaO · Al ₂ O ₃ is generated by the reduction reaction of chromium oxide, but the amount of lime is not as high as that of the silicon reduction method. Therefore, the amount of lime used can be reduced.

  The raw material was charged in a 500 kVA arc melting furnace with 45 kg of chromium oxide, 9 kg of quicklime, and 17.4 kg of aluminum. Then, the graphite electrode was energized to dissolve the raw material, and the reduction reaction of chromium oxide was advanced to obtain 29.5 kg of primary metal and 26.0 kg of primary slag.

The composition of the primary metal was as shown in Table 1 below.

一次スラグの排出後、一次メタル２９．５ｋｇに生石灰９ｋｇを添加し、アーク溶解炉に再通電した。生石灰を溶解して二次スラグを形成し、二次スラグによって金属溶融を酸化精錬した。二次メタルの成分組成は以下の表３のとおりである。

Next, the arc melting furnace was tilted to discharge the primary slag made of calcium aluminate. The composition of the primary slag is as shown in Table 2 below. After cooling, primary slag was used as a desulfurization agent for steelmaking.

After discharging the primary slag, 9 kg of quicklime was added to 29.5 kg of the primary metal, and the arc melting furnace was re-energized. Quick lime was dissolved to form secondary slag, and the metal smelt was oxidized and refined by the secondary slag. The composition of the secondary metal is as shown in Table 3 below.

  The arc melting furnace was tilted to discharge the secondary metal and secondary slag into the mold. After cooling, the secondary slag adhering to the surface of the secondary metal was removed by shot blasting.

  The ingot of metal chromium was crushed to 40 mm or less by a crusher and charged into a vacuum heating furnace. Then, it cooled to normal temperature in the vacuum heating furnace, and the ingot of metal chromium was taken out from the vacuum heating furnace. Carbon, oxygen, and nitrogen were removed by vacuum heat treatment. The metal chromium finally obtained was high-purity metal chromium with few impurities.

This specification is based on Japanese Patent Application No. 2012-135698 of an application on June 15, 2012. All this content is included here.

Claims (5)

A process of charging chromium oxide, aluminum, and lime as raw materials into an electric furnace;
Energizing the electric furnace to dissolve the raw material, reducing the chromium oxide with aluminum, and generating a primary metal and primary slag containing chromium;
Tapping the primary slag from the electric furnace;
Adding a basic flux to the primary metal of the electric furnace;
Electrifying the electric furnace to dissolve the basic flux, oxidizing and removing aluminum remaining in the primary metal, and generating a secondary metal;
A method for producing metallic chrome.   The method for producing metallic chromium according to claim 1, wherein the content of chromium in the primary slag separated from the primary metal is less than 1.0 mass%.   The said primary slag is the calcium aluminate which has CaO and Al2O3 as a main component, The manufacturing method of the metal chromium of Claim 1 or 2 characterized by the above-mentioned.   The metallic chromium according to any one of claims 1 to 3, wherein the secondary metal has an aluminum content of 0.02 mass% or less and an iron content of 0.20 mass% or less. Production method. The method for producing the metal chromium further includes:
Tapping and casting the secondary metal of the electric furnace;
Crushing the cast secondary metal;
The method for producing metallic chromium according to any one of claims 1 to 4, further comprising a step of degassing the crushed secondary metal to obtain metallic chromium.

Images