JPS60211006A - Manufacture of reduced iron - Google Patents

Abstract

PURPOSE:To obtain reduced iron with high productivity by mixing iron oxide powder with a specified amount of a specified alkali metallic compound and reducing the mixture with solid carbon as a reducing agent. CONSTITUTION:Iron oxide powder such as mill scale is mixed with 0.5-30wt% one or more kinds of compounds selected among the carbonates, hydrogencarbonates, sulfates, nitrates, acetates, sulfides, halides, oxides and hydroxides of alkali metals such as Na. The mixture is heated together with solid carbon such as coke as a reducing agent to obtain reduced iron. It is desirable that the mixture is heated after putting the mixture in a vessel in the form of a hollow cylinder and packing the solid carbon into the inner and outer spaces. By this method the time required to reduce iron oxide can be shortened to about 1/2- 1/3, and productivity can be considerably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly productive method for producing reduced iron by reducing iron oxide powder with a solid carbon reducing agent.

Traditionally, iron powder for powder metallurgy and iron powder for welding rods have been made by mixing iron oxide powder such as iron ore or mill scale with a solid carbon reducing agent such as coke and, if necessary, lime in a heat-resistant container called a sagger. It is manufactured by heating the iron in a tunnel furnace to produce reduced iron, which is then crushed.

Such an iron powder manufacturing method requires a long time for reduction in a tunnel furnace, making it difficult to increase productivity. Therefore, various studies have been made to improve productivity and reduce manufacturing costs. That is, methods such as using charcoal, which has extremely good reactivity as a solid carbon reducing agent, and mixing a solid carbon reducing agent such as coke into iron oxide powder (Japanese Patent Publication No. 48-32885) have been proposed. However, charcoal becomes CO gas at low temperatures where the iron oxide powder is not reduced, and the amount of solid charcoal decreases, making it difficult to maintain the initial filling shape of the iron oxide powder, and during reduction, the iron oxide powder spreads and reacts. Problems such as the extremely thick layer resulting in a long reaction completion time or, in the worst case, the iron oxide powder collapsing and adhering to the inner wall of the sagger, have arisen.

In addition, with the method of mixing solid carbon reducing agents such as coke into iron oxide powder, it is difficult to fill the sago uniformly without segregation after mixing the two, which have a large difference in specific gravity, and float and separate during filling. easy. As a result, since the upper part of the obtained reduced iron contains a large amount of floating solid carbon reducing agent, reduction proceeds quickly and tends to be overcarburized. On the other hand, in the lower part of the reduced iron, the solid carbon reducing agent floats and separates and decreases, which tends to result in poor reduction. Furthermore, in order to remove the ash content in the solid carbon reducing agent remaining in the reduced iron, a powerful magnetic separation process is required, and it is also necessary to select an expensive solid carbon reducing agent with a low ash content. In addition, if ash remains in the iron powder, compressibility deteriorates,
This causes a decrease in strength and poor machinability after sintering.

An object of the present invention is to eliminate the drawbacks of the above-mentioned conventional methods and to provide a method for producing reduced iron with high productivity using inexpensive means.

In the method of the present invention, a specific alkali metal compound is added and mixed in advance to iron oxide powder, and this mixture is reduced with a solid carbon reducing agent to produce reduced iron at low cost and with high productivity.

Alkali metals are contained in small amounts in iron ore and coke, which are charged into blast furnaces, and are known to have a negative effect on the softening and melting of iron ore and the reduction in strength of coke. Also,
Accumulated and concentrated alkali was thought to cause damage to furnace wall bricks, and was viewed as a problem.

However, the presence of alkali increases the reactivity of the coke and increases the rate of reduction of iron oxide.

The inventor of the present invention has discovered the present invention as a result of intensive studies on the type and type of alkali.

That is, carbonates, bicarbonates, sulfates, and nitrates of alkali metals mixed in advance with iron oxide powder.

Acetate, sulfide, halide, oxide, or hydroxide melts at around 100° C. and evaporates as it is, or is reduced to an alkali metal by CO gas generated from the solid carbon reducing agent and evaporates. As a result, the portions where these alkali metal compounds mixed in the iron oxide powder existed remain as pores communicating with the solid carbon reducing agent, and CO gas easily diffuses through these pores, resulting in rapid reduction. do. In addition, a part of the evaporated alkali metal causes cracks in the solid carbon reducing agent in contact with the iron oxide powder, increasing its reactivity and reducing CO2.
Further promote gasification. Therefore, the reduction time can be significantly shortened without the alkali metal compound remaining in the reduced iron. Furthermore, since these alkali metal compounds have some unique hygroscopicity, they can be added uniformly to the iron oxide powder without floating and separating when filling the solid carbon reducing agent, and the reduction of the upper and lower portions of the reduced iron is reduced. On the other hand, as a solid carbon reducing agent, it is desirable to use a fine material with good reactivity and a high filling rate, containing 85% by weight or more of particles with a particle size of 1.0 mm or less. , 2 to 50% by weight of alkali metal compound if not fine.
A mixed solid carbon reducing agent may be used. More preferably, a fine solid carbon reducing agent is mixed with an alkali metal compound in an amount of 2 to 50% by weight. Particle size 1
．． A fine solid carbon reducing agent containing 85% by weight or more of particles of 0 m or less has a high filling rate for the following reason.

In general, the smaller the particle size of solid particles, the larger the pore volume and the lower the apparent density. As the grain size increases, the reduction in apparent density due to the influence of pores becomes more relaxed, and as a result, the grain size decreases to 1. When the content of particles of 0m or less is 85% by weight or more, the apparent density suddenly increases. Therefore, the fine solid carbon reducing agent reduces the required filling volume into a heat-resistant container, making it possible to increase the amount of iron oxide powder filled, thereby improving the productivity of reduced iron. . At the same time, due to the large surface area and high apparent density of the fine solid carbon reducing agent, the rate of generation of CO gas during reduction is high, and the diffusion of CO gas into the iron oxide powder is promoted, thereby improving the reduction rate.

Further, a fine solid carbon reducing agent containing 85% by weight or more of particles of 1,000 m or less has the advantage that the surface of the obtained reduced iron has no irregularities, and post-processing steps such as brushing can be omitted. The alkali metal compound in the solid carbon reducing agent serves to generate cracks in the solid carbon reducing agent, increase the surface area, and promote CO gasification, and has a different effect from those mixed in iron oxide powder.

Next, the reasons for the limitations of the present invention will be described.

As an alkali metal compound, price, effect when added,
The above-mentioned alkali metal carbonates, hydrogen carbonates, sulfates, nitrates, acetates, sulfides, halides, oxides, and hydroxides are preferred from the viewpoint of ease of addition. Solid substances may be mixed as they are with iron oxide powder or solid carbon reducing agent, and highly deliquescent hydroxides may be immersed in an aqueous solution of a specific concentration for a required period of time, and then dried to adjust the amount added.

Addition amount of alkali metal compound to iron oxide powder is 0.5
If the amount is less than 3% by weight, there will be no noticeable difference compared to the case without addition, and if the amount added exceeds 3Qqjφ%, the packing density of the iron oxide powder will decrease and large pores will remain in the reduced iron after reduction. Weight per unit length of reduced iron obtained by
is smaller than in the case without additives, making it impossible to improve productivity.

In carrying out the present invention, a mixture of iron oxide powder and the specific alkali metal compound is filled in a container in a cylindrical shape, and the outside of the container is filled with a solid carbon reducing agent and heated. In this way, it is possible to obtain a reduction reaction progress rate approximately twice as high as that of additive-free iron oxide powder.

Alternatively, if the above mixture is filled in a container in a hollow cylindrical shape, and a solid carbon reducing agent is filled inside and outside of the container and heated,
Since the thickness of the reduced layer can be reduced, the reduction time can be further shortened.

According to the present invention, the reduction time for reduced iron can be shortened to that required for conventional repairs.

Example 1 Sodium carbonate (Na2C
Mill scale 2 containing 2% by weight of O3) was 75 m in diameter.
Filled in a cylindrical shape with particle diameter of 1. Coke 3 containing 92% by weight of particles smaller than Om m was charged. In addition,
As a comparative example, mill scale 2 without additives was placed in a container of the same size.
and particle size 1. Coarse coke 3 with a content of 47% by weight or less was similarly charged. After that, it was carried into the electric furnace and 11
The temperature was raised to 00°C, maintained for 6 to 40 hours, and then cooled in a furnace. The weight of the obtained reduced iron was measured, and the reduction rate was calculated from the change in weight. FIG. 2 shows the relationship between the reduction time and the reduction rate for Examples and Comparative Examples. In the comparative example, the reduction rate is 1
While 40 hours of reduction time is required to achieve 00% reduction, in the embodiment of the method of the present invention, 100% reduction was achieved in about 20 hours.
can achieve a return rate of From this, it can be seen that the method of the present invention completes the reduction in about half the reduction time compared to the conventional method.

Example 2 5% by weight of NaOH by immersing in 5N sodium hydroxide (NaOH) aqueous solution for 15 minutes or more and then drying.
The contained mill scale was filled into a cylindrical shape with a wall thickness of 30 mm in the same heat-resistant container as in Example 1, and 10% by weight of sodium chloride (Na0 content) was added and mixed inside and outside the container.
Coke containing 47% by weight of particles smaller than mm was filled.

As a comparative example, additive-free mill scale and additive-free coke of the same particle size were used and filled in the same manner.

When each of the samples was reduced at 100° C. for 15 hours, the reduction rate in the method of the present invention was 100%, and the reduction rate in the conventional method was 55%, which was a large difference in the reduction rate.

Example 3 Sodium sulfide (Na2S) was placed in the same heat-resistant container as in Example 1.
) Particle size: 1.0% by weight of hematite-based iron ore and 5% by weight of soda lime (Na20+Cao). O
Coke containing 92% by weight of less than mm was filled into a hollow cylinder in the same manner as in Example 2, and reduced at 1100 degrees. In addition,
As a comparative example, additive-free hematite iron ore and particle size 1.0
Coke containing 47 wt. Similar to FIG. 2, FIG. 3 shows the relationship between the reduction time and the reduction rate. The hematite iron ore of the comparative example required 40 hours to achieve a reduction rate of 100%, but the method of the present invention achieved a reduction rate of 10% in about 13 hours.
0%, which shortened the return time to approximately the same amount.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the filling state of mill scale and coke in Example 1 of the method for producing reduced iron of the present invention, and FIGS. 2 and 3 are the reduction time and reduction rate in Example 1 and Example 3, respectively. This is a graph showing the relationship between l...Heat-resistant container 2...Mill scale 3...Coke applicant Kawasaki Steel Co., Ltd. Agent Patent attorney Yoshi Kosugi Male patent attorney Kazunori Saito Figure 1 (Q) (b) Figure 2 To 17: g! ! F lock (11rJ Fig. 3

Claims (1)

[Claims] l Iron oxide powder containing one or more of alkali metal carbonates, hydrogen carbonates, sulfates, nitrates, acetates, sulfides, /\logenides, oxides, or hydroxides. .5% by weight or more3
A method for producing reduced iron, which comprises adding and mixing 0% by weight or less, and heating the mixture together with a solid carbon reducing agent. 2. Claim 1, in which the mixture is filled in a container in a cylindrical shape, and a solid carbon reducing agent is filled on the outside of the container and heated.
The method for producing reduced iron described in Section. 3. The method for producing reduced iron according to claim 1, wherein the mixture is filled in a container in a hollow cylindrical shape, and the inside and outside of the container are filled with a solid carbon reducing agent and heated.