JP6188690B2 - Ferrochrome production method and ferrochrome - Google Patents

Description

  The present invention relates to a method for producing ferrochrome and ferrochrome, and more particularly to a method for producing ferrochrome having a low cobalt content and ferrochrome.

  Ferrochrome alloys are generally manufactured by a method of reducing chromium ore with silicon, and a so-called Perran method is adopted as a specific method thereof. As shown in FIG. 3, the basic process of this Peran method is to dissolve chromium ore containing chromium oxide and iron oxide and calcined lime, which is a solvent medium, in an electric furnace, and use the molten synthetic slag as a ladle. The hot water is discharged, and the auxiliary raw material silicochrome is added to the ladle as a reducing agent and stirred to cause a reduction reaction. Then, the slag (secondary slag) is separated to obtain a molten ferrochrome, and the molten ferrochrome is cast into a mold to obtain a product ferrochrome. The separated secondary slag is disposed of separately (see Patent Document 1).

JP-A-5-51690

  By the way, in recent years, a need for a chromium material having a low cobalt content has been increasing in order to eliminate problems caused by the incorporation of cobalt into products such as stainless steel. However, the chromium ore used for the production of ferrochrome contains 0.015 to 0.120% by mass of cobalt, and the auxiliary raw material silicochrome contains 0.015 to 0.040% by mass of cobalt. Cobalt has a property that it is very easily reduced compared to chromium, and is reduced preferentially over chromium, so that almost the entire amount of cobalt in the raw material is transferred to the product metal. For this reason, in the conventional manufacturing method of ferrochrome, it was impossible to make the cobalt quality in ferrochrome 0.050 mass% or less.

  Only the metal chromium produced by using chromium oxide obtained by subjecting chromium ore to chemical treatment (see Japanese Patent No. 3338701) can meet the needs for chromium materials having a low cobalt content. There is a problem of becoming an expensive chromium material.

  Then, an object of this invention is to provide the manufacturing method and ferrochrome which can manufacture the low cobalt ferrochrome by a cheap and simple method.

  In order to solve the above problems, an embodiment of the present invention includes a step of melting chromium ore and calcined lime in a furnace to generate synthetic slag, a reducing agent added to the synthetic slag, and a cobalt oxide in the synthetic slag. And reducing the chromium oxide and iron oxide in the slag by adding a reducing agent to the separated slag, the step of separating the cobalt-containing alloy and slag, the step of separating the cobalt-containing alloy and slag And the process of producing | generating ferrochrome, The manufacturing method of ferrochrome provided with.

  According to the present invention, cobalt is separated from synthetic slag, and ferrochrome is produced using low-cobalt slag from which cobalt is separated, so that the quality of cobalt can be achieved without using expensive chemical-treated raw materials. Low ferrochrome can be obtained.

Process drawing of the manufacturing method of ferrochrome of one Embodiment of this invention The graph which shows the relationship between the reducing agent ratio of the reducing agent added in the synthetic slag of this embodiment, and a decomponent ratio Process diagram of conventional ferrochrome production method

  Hereinafter, the manufacturing method of the ferrochrome of one Embodiment of this invention is demonstrated based on an accompanying drawing. FIG. 1 is a process chart of a method for producing ferrochrome according to this embodiment. The method for producing ferrochrome of the present embodiment is roughly divided into three steps: a step of producing low cobalt slag (hereinafter referred to as step I), a step of producing low cobalt ferrochrome (hereinafter referred to as step II), And a step of recovering silicochrome (hereinafter referred to as a silicochrome recovery step).

  In Step I, first, a mixture of chromium ore and burnt lime as a solvent is dissolved in an electric furnace to generate synthetic slag (S1). Next, the synthetic slag melted in the electric furnace is discharged into the ladle 1. Then, an aluminum or silicon-containing alloy reducing agent (ferrosilicon in this embodiment) is added to the molten synthetic slag of the ladle 1, and stirred for 2 to 10 minutes (S2). Silicochrome or aluminum can be used as the reducing agent in addition to ferrosilicon, but it is desirable to use ferrosilicon because it is inexpensive.

The amount of the reducing agent added is the theoretical reducing agent necessary for reducing the total amount of oxides (chromium oxide (Cr ₂ O ₃ ), iron oxide (FeO) and cobalt oxide (CoO)) in the synthetic slag. The amount corresponds to 15 to 40% of the amount. At this time, cobalt is preferentially reduced by the free energy difference during reduction. The order in which they are easily reduced is the order of cobalt, iron, and chromium. Cobalt can be preferentially reduced by making the amount of the reducing agent less than the theoretical amount of the reducing agent. A small amount of the preferentially reduced cobalt-containing alloy settles on the bottom of the ladle 1 due to the specific gravity difference.

  When the stirring time is less than 2 minutes, the cobalt quality in the synthetic slag is not lowered, but rather the chromium quality is slightly lowered, and the cobalt quality and the chromium quality are not stable. Since the cobalt quality in the synthetic slag is sufficiently reduced within the stirring time of 10 minutes, the stirring time is desirably 2 to 10 minutes.

The supernatant slag is a low-cobalt slag containing less than 0.01% by mass of cobalt. In Step II, in order to separate the supernatant slag and the cobalt-containing alloy, only the supernatant slag is transferred to another ladle 2 (S3). Then, a low cobalt ferrochrome is produced using a reducing agent containing silicon (silicochrome in this embodiment) in the same manner as normal low carbon ferrochrome. That is, silicochrome is added as a reducing agent to the ladle 2 charged with the supernatant slag, and chromium oxide and iron oxide in the supernatant slag are reduced to generate low cobalt low carbon ferrochrome and secondary slag. The amount of silicochrome added as the reducing agent is greater than the theoretical amount of reducing agent required to reduce the total amount of oxides (chromium oxide (Cr ₂ O ₃ ), iron oxide (FeO)) in the supernatant slag. is there. The secondary slag produced by the reduction reaction is separated from the low-carbon ferrochrome melt and transferred to the ladle 3 (S4). The low-cobalt low-carbon ferrochrome melt obtained by separating the secondary slag is cast into a mold to become a product. The cobalt concentration of the low carbon ferrochrome depends on the cobalt concentration of the reducing agent used in Step II, but is generally less than 0.030% by mass.

The cobalt-containing alloy generated in step I is discharged into the ladle 3 used in the silicochrome recovery step. As described above, the secondary slag is previously charged in the ladle 3, and the cobalt-containing alloy is mixed with the secondary slag. In the silicochrome recovery step, ferrosilicon as a reducing agent and aragonite are added to the ladle 3 and agitated to reduce chromium oxide remaining in the secondary slag to produce high cobalt silicochrome. This high-cobalt silicochrome is used as a raw material when producing a variety that does not pose a problem even if the cobalt concentration is high. The final slag produced by the silcochrome production operation is separated and removed. The reason why the meteorite is added to the ladle 3 is to adjust the CaO / SiO ₂ ratio of the final slag.

  In addition, the stirring method in the reduction operation of step I performed to promote the reaction, the stirring method in the reduction operation of step II, and the stirring method in the reduction operation of the silicochrome recovery step may be relay ring or gas blowing (Bubbling method) may be used.

  Synthetic slag consisting of chrome ore and calcined lime melted in a 6,000kVA Eru-type electric furnace and receiving 11,040kg of synthetic slag of 0.046% in the ladle, 300kg corresponding to 22% of the theoretical reducing agent amount. Of ferrosilicon was added, and after stirring for 7 minutes, 10,288 kg of supernatant slag was collected in another ladle. The cobalt grade of this slag showed a low value that could not be detected by an analyzer that could detect up to 0.001%.

  Further, 2,050 kg of silicochrome was added to the ladle which received the low cobalt slag, and 3,470 kg of the chromium alloy obtained by stirring for 10 minutes was cast into a mold and recovered. The cobalt grade of this chromium alloy was as low as 0.024%.

  Table 1 compares the quality of chromium, iron, and cobalt in the conventional low-carbon ferrochrome production method (conventional operation) shown in the figure and the low-carbon ferrochrome production method of the present invention example (new operation). . The synthetic slag in the table is generated by melting chromium ore and calcined lime in an electric furnace. Low cobalt slag is produced by reducing synthetic slag. Slag after product recovery is the secondary slag generated in Step II. The final slag is slag generated in the silicochrome recovery process. At the bottom of Table 1, the grade of chromium, iron and cobalt of the low carbon ferrochrome of the product is also described.

  As shown in Table 1, in the conventional method for producing low-carbon ferrochrome (conventional operation), the cobalt quality in the synthetic slag is 0.046%, and the cobalt quality in the low-carbon ferrochrome of the product is 0.108%. Met. It can be seen that cobalt is reduced and transferred to the product.

  In contrast, in the method for producing low carbon ferrochrome of the present invention example (new operation), even if synthetic slag of the same component is used, the quality of cobalt in the low carbon ferrochrome of the product is reduced to 0.024%, Reduced to 1/4 to 1/5 of the cobalt grade in low carbon ferrochrome in operation. This is because low carbon ferrochrome is produced using low cobalt slag. The iron grade in the low cobalt slag was 3.7%, and the cobalt grade was 0.002%. The cobalt quality in the low carbon ferrochrome of the product was 0.024%, and the iron quality in the low cobalt slag decreased, and the cobalt quality in the low carbon ferrochrome increased to 70% or more.

FIG. 2 shows the experimental results of the relationship between the reducing agent ratio of the reducing agent added to the synthetic slag and the decomponent ratio. The reducing agent ratio on the horizontal axis of the graph of FIG. 2 is the theoretical amount for reducing the total amount of oxide (Cr ₂ O ₃ , FeO and CoO) in the reducing agent input amount / synthetic slag. The decomponent rate on the vertical axis is 1-component mass in the slag after reduction / component mass in the slag before reduction. The decomponent rate means the proportion of cobalt removed from the synthetic slag. The larger the decomponent ratio, the more cobalt is removed from the synthetic slag and it is reduced to metal. In FIG. 2, the decomponent ratios of iron, cobalt, and chromium are plotted as で, Δ, and □, respectively.

  As shown in FIG. 2, when the reducing agent ratio is less than 15%, the reduction of iron, cobalt, and chromium did not proceed. It is assumed that the reducing agent is used to remove oxygen involved in the raw material when the raw material is dissolved in the electric furnace. When the reducing agent ratio is 15% or more, the decomponent ratio of cobalt in the synthetic slag increases, and when the reducing agent ratio exceeds 20%, the decomponent ratio of cobalt exceeds 80%. When the reducing agent ratio is further increased, the increase rate of the decomponent rate decreases, but the decomponent rate approaches 100%. As the reducing agent ratio increases, the decomponent ratio of iron also increases, but the decomponent ratio does not increase as much as cobalt. Even when the reducing agent ratio increases, the component removal rate is almost zero. It can be seen that cobalt is preferentially reduced by the difference in free energy during reduction.

  This specification is based on Japanese Patent Application No. 2012-135697 of an application on June 15, 2012. All this content is included here.

Claims (2)

Melting chrome ore and calcined lime in a furnace to produce synthetic slag;
Adding a reducing agent to the synthetic slag, reducing cobalt oxide in the synthetic slag, and generating a cobalt-containing alloy and slag;
Separating the cobalt-containing alloy and slag;
Adding a reducing agent to the separated slag, reducing chromium oxide and iron oxide in the slag, and generating ferrochrome;
Mixing the cobalt-containing alloy separated from the slag with secondary slag separated from the ferrochrome in the step of generating the ferrochrome;
Reducing the chromium oxide remaining in the secondary slag with a reducing agent containing silicon, and recovering silicochrome containing cobalt . In the step of generating the cobalt-containing alloy and the slag,
The method for producing ferrochrome according to claim 1, wherein a reducing agent corresponding to 15 to 40% of a theoretical reducing agent amount required for reducing the total amount of oxide in the synthetic slag is added.

Images