JPH0794681B2 - Method for producing iron powder from converter dust - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing high-quality iron powder from dust in a steelmaking converter by a simple treatment process.

[Prior Art] A large amount of dust is generated in a steelmaking converter in an iron mill. For example, in the wet dust collection process, the amount of dust generated may reach about 1000 tons / month for one 180 ton converter. This dust contains about 60 to 70% of metallic iron and has high iron quality, but also contains a large amount of slag components such as graphite, CaO, and SiO ₂ .

In the past, such converter dust was usually used as a part of raw material for sinter or pellets for blast furnace from the viewpoint of recovering the iron source. Recently, attempts have been made to produce iron powder with higher added value from this converter dust.

Metallic iron powder has various uses such as powder metallurgy, welding rod, and cutting, and various characteristics are required, but at present, most of these industrially used iron powders are atomized or reduced. Manufactured by law.

However, since the manufacturing process is complicated and expensive raw materials, a large amount of energy, and other expensive auxiliary materials such as atomized gas are required, there is a limit to inexpensively producing high-grade iron powder.

For this reason, it would be advantageous if high-quality iron powder could be produced from converter dust, which is a by-product of steelmaking.

Several methods have been proposed in the past for recovering iron powder from converter dust. For example, Japanese Examined Patent Publication (Kokoku) No. 57-44724 discloses a method for recovering iron powder, which comprises pulverizing converter dust by wet pulverization and then performing magnetic separation to separate the powder.

Further, in JP-A-59-1602, after pulverizing converter dust, magnetic force is selected, and the surface impurity layer of the obtained iron powder is 0.3 to
Disclosed is a method for producing iron powder, which comprises treating with a 0.9 normal mineral acid and subjecting it to impact compression grinding.

[Problems to be Solved by the Invention] Although the methods proposed in the above publications are considered to be advantageous methods for producing iron powder, they completely remove impurities such as graphite and slag components accompanying converter dust. There is a limit to the separation. In particular, although magnetic force selection is performed by any of the methods, fine particles of impurities mixed in the dust become entangled with the iron powder and magnetize the iron powder and the iron powder, which deteriorates the quality of the iron powder.

Further, in JP-B-57-44724, wet pulverization is carried out, but during this wet pulverization, the surface of the metallic iron powder is significantly oxidized to form an oxide scale layer, which requires a reduction treatment step or an oxidation treatment step. As a result, the manufacturing process becomes complicated, the yield of iron powder decreases, and the cost inevitably increases.

The present invention is intended to inexpensively produce high-grade and high-value iron powder from converter dust that completely separates impurities such as graphite and slag components without performing a magnetic separation step and a wet milling step. is there.

[Means for Solving the Problem] That is, the present invention comprises: (a) a first step of classifying the collected converter dust to classify particles having a particle size of 20 to 500 μm;
(B) The second step of pulverizing and grinding the separated granules with a dry pulverizer to remove the deposits such as graphite and slag on the surface layer of the particles, and (c) the inclination of the granules after the pulverization and grinding. 5 corners
Iron powder from converter dust, which comprises a third step of dispersing and dropping onto a slope of 40 °, collecting iron powder on the falling ore side, and separating and removing graphite and slag on the residual ore side. Related to the manufacturing method of.

Further, the present invention includes (a) a first step of classifying the converter dust collected by a dust collector to classify granules having a particle size of 20 to 500 μm, and (b) dry granulation of the granules after classification. The second step of crushing and grinding by a machine to remove the deposits such as graphite and slag on the surface layer of the particles, and (c) the particles after crushing and grinding are dispersed and dropped on the slope with an inclination angle of 5 to 40 °. Then, the iron powder is collected on the falling ore side, the third step of separating and removing the graphite and slag from the residual ore side, and (d) the iron powder on the falling ore side is treated with a 1-10 N hydrochloric acid aqueous solution. The present invention relates to a method for producing iron powder from converter dust, which comprises a fourth step.

[Function] The converter dust that is carried away in the exhaust gas during steelmaking of the converter and collects the converter dust is of a coarse particle size within a certain particle size range and other fine particle size or oversize particle size. The shape characteristics are also distributed in different states, and if you select particles with a particle size in a specific range, it is easy to carry out secondary treatment of high iron quality that cannot be obtained with particles with other particle sizes. It was found that granular iron powder was obtained.

Table 1 below shows the physical shapes of the iron powder (coarse iron powder and ultrafine iron oxide powder), graphite and lime present in the converter dust.

As shown in Table 1, in the converter dust, coarse iron powder having a particle size in the range of 20 to 500 μm exists in the dust as it is generated, which is a fine iron oxide powder or graphite. Since there is a great difference in size and shape from lime and the like, simple substances can be separated. This coarse iron powder is in a state where oxide scale, graphite and slag components are attached to the surface of spherical metallic iron coarse particles.

This is because the droplets of steel scattered from molten steel during converter steelmaking solidify in a spherical state due to its surface tension, and an oxide film is formed on the surface during flight or in a dust collector, and it accompanies the exhaust gas. This is probably because there occurs a phenomenon that substances other than steel such as slag and graphite adhere to the surface.

If the surface of this coarse iron powder is ground and ground using a dry pulverizer, the graphite and slag adhering to the surface will be separated from the surface of the spherical metallic iron coarse particles as fine powder with a size of less than 44 μm. I understood.

The metallic iron coarse particles have a large difference in size and shape from the exfoliated graphite and slag, and in this respect, they exist in a form that allows easy separation of simple substances.

The method of the present invention utilizes the characteristics of the physical properties of converter dust as described above.

In the first step of the present invention, the converter dust collected by a dust collector or the like is classified to separate particles having a particle size of 20 to 500 μm. By this separation, it is possible to separate fine powder with a low iron quality and a high iron oxide content of less than 20 μm from coarse powder with a low iron quality and a large grain size of more than 500 μm with a large amount of graphite and lime particles, which results in a high iron recovery yield. Thus, iron, that is, coarse iron powder, can be collected from the converter dust.
The classification treatment may be of any type as long as it can classify particles having a particle size of 2.0 to 500 μm from converter dust, but a wet classification method is suitable.

In the second step, the particle size separated in the first step is 20 to 500
Grain particles having a diameter of μm are crushed and ground by a dry crusher to remove adhered substances such as graphite and slag on the surface layer of coarse iron powder. As the crusher used, a dry ball mill, a vibration mill or the like can be used. When a wet pulverizer is used, the metal surface is oxidized during the wet pulverization to form an oxide scale layer,
It is not preferable because the yield of iron powder decreases. Although the degree of grinding ore treatment is not particularly limited, when the grinding ore is insufficient, the exfoliation of graphite and slag becomes insufficient, and the iron quality of the obtained metal iron powder deteriorates. If the ore is excessively added, a part of the metallic iron particles will be crushed, and it will be mixed with graphite and slag to reduce the yield of metallic iron powder, which is not preferable. That is, only the graphite and slag components on the surface of the metallic iron coarse particles are crushed, peeled off, and crushed and ground so that the metallic iron coarse particles remain the original spherical coarse particles. Is advantageous in terms of purity and yield.

In the third step, by utilizing the large difference in shape between the metallic iron particles and the exfoliated graphite or slag in the particles after the grinding and grinding in the second step, the particles after the grinding and grinding are placed on the slope. Dispersed and dropped into the
On the residual ore side, graphite and slag are separated and removed (hereinafter, this step is referred to as slope drop selection). That is,
Since only spherical metallic iron particles roll down on the slope and fall, and amorphous graphite and slag are retained on the slope, the metallic iron particles can be separated on the falling side. At this time, the inclination angle of the slope must be 5 to 40 °. If the tilt angle is less than 5 °, it is not preferable because the metallic iron particles remaining on the slope significantly increase, and the tilt angle is 40 °.
If it exceeds, the amorphous graphite and slag will fall on the slope and fall, and the iron quality of the iron powder will deteriorate. It is desirable that the feed rate of the granules after grinding and grinding on the slope be as slow as possible. When a large amount of crushed and ground granules are supplied to the slope at once, the spherical metallic iron particles and the amorphous graphite and slag are intertwined and fall on the slope, and the graffiti and slag on the falling side. This is not preferable because it causes a harmful effect of mixing the components.

It is desirable that graphite and slag remaining on the slope be appropriately removed so as not to obstruct the fall of the metallic iron particles.

Further, the surface material of the slope is not particularly limited, but it is desirable that the slope has a surface roughness such that relatively fine graphite or slag can be retained on the slope.

It is possible to obtain iron powder containing 94% by weight or more of metallic iron from converter dust only by passing through the first step, that is, the classification step, the second step, that is, the crushing and grinding step, and the third step, that is, the slope drop selection step. it can.

The obtained iron powder can be used as an industrial iron powder as it is, but in order to obtain a higher quality iron powder, the iron powder on the falling ore side is added with 1 to 10N hydrochloric acid in the fourth step. Can be treated with hydrochloric acid. As a result, the oxide scale layer existing on the surface of the iron powder can be eluted, and the high-quality iron powder containing 98% by weight of metallic iron can be obtained. In this case, considering the neutralization of the acid by the basic compound such as CaO mixed in, it is necessary to treat the acid with a strong acid having a concentration of 1 N or higher. Hydrochloric acid is used as the acid. Acids having oxidizing power, such as sulfuric acid and nitric acid, are not preferable because they oxidize and passivate iron at high concentrations. The oxide scale layer can be sufficiently eluted without using concentrated hydrochloric acid that exceeds 10 N.

As described above, the present invention does not carry out the magnetic separation step or the wet fine pulverization step, and the coarse iron powder present in the converter dust is separated from the metallic iron particles by the pulverizing grinding mill in the graphite, and the slag is separated. Separation, yet the iron and iron particles are separated from the converter dust by utilizing the large difference in the shape that the metallic iron particles have a spherical shape, whereas the graphite and the slag have a relatively fine amorphous shape. Classification
The feature is that high value-added iron powder can be manufactured by a simple and economical process of crushing and slope drop selection.

[Examples] Hereinafter, the method of the present invention will be further described with reference to Examples.

Example 5 kg of converter dust collected by a dust collector was wet classified with a Taylor standard sieve in the form of generation to separate particles having a particle size of 20 to 500 μm. The obtained granules were kept at 100 to 120 ° C. for 3 hours to be dried, and then pulverized at a dry mill using a vibration mill for about 3 minutes. Further, the particles after crushing and grinding were dispersedly dropped onto a slope having an inclination angle of 20 ° to separate the falling ore and the residual ore. As the slope, a low carbon cold rolled steel sheet having a surface roughness of 10 μm was used.

The converter dust tested, the dry classified product collected by the classification in the first step, and the iron powder obtained on the falling ore side by the slope drop selection in the third step were analyzed, and the results shown in Table 2 were obtained. It was

As can be seen from the results in Table 2, even if the converter dust remains in the generated form, metallic iron (M.Fe) becomes 81.5% by weight only by separating 20 to 500 μm particles, It can be seen that the quality of metallic iron improves to 94.6% by weight.

The slope drop selection was performed using slopes with slope angles of 5 ° and 40 ° instead of slopes with slope angle of 20 °, and similar results were obtained.

Further, the granules obtained on the falling side of the slope drop screening were leached in 1.5 l of 5 N hydrochloric acid with mechanical stirring for 3 minutes, then, leached, and the residue was dried. The components of the dried granules are also shown in Table 2. As shown in Table 2, this granular material contains metallic iron.
It was 98.3% by weight of high-grade iron powder.

The treatment was performed using 1N and 10N hydrochloric acid instead of 5N hydrochloric acid, but the results were the same.

A micrograph of iron powder treated with 5N hydrochloric acid is shown in FIG. As seen in FIG. 1, it can be seen that this iron powder is a powder having a spherical shape.

Further, Table 2 shows representative components of commercially available reduced iron powder for comparison, but it is understood that the iron powder produced by the method of the present invention is comparable in composition.

[Effects of the Invention] As described above, according to the method of the present invention, spherical high-grade iron powder can be produced from converter dust by a simple and small number of steps of classification, pulverization, and slope drop selection. By performing the hydrochloric acid treatment in the fourth step depending on the intended use of (1), a higher quality iron powder can be obtained.

Therefore, the converter dust, which is a by-product of steelmaking, can be economically added as an industrial iron powder suitable for cutting, welding rods, powder metallurgy, and the like.

[Brief description of drawings]

FIG. 1 is a micrograph (magnification × 100) showing the particle structure of iron powder obtained in the examples.

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Claims (2)

[Claims] 1. A first step of (a) classifying the collected converter dust to classify particles having a particle size of 20 to 500 μm, and (b) crushing the particles after classification with a dry crusher. Mine,
A second step of peeling off the deposits on the surface layer of the particles, (c) the particles after grinding and grinding are dispersedly dropped onto a slope having an inclination angle of 5 to 40 °, and iron powder is collected on the falling side, A method for producing iron powder from converter dust, comprising a third step of separating and removing graphite and slag on the residual ore side. 2. A first step of: (a) classifying the collected converter dust to classify particles having a particle size of 20 to 500 μm; and (b) crushing the particles after classification with a dry crusher. Mine,
A second step of peeling off the deposits on the surface layer of the particles, (c) the particles after grinding and grinding are dispersedly dropped onto a slope having an inclination angle of 5 to 40 °, and iron powder is collected on the falling side, A transfer process characterized by comprising a third step of separating and removing graphite and slag on the residual ore side, and (d) a fourth step of treating iron powder on the falling ore side with a 1-10 N hydrochloric acid aqueous solution. Method for producing iron powder from furnace dust.