JPH06279824A - Production of iron powder utilizing microwaves - Google Patents

Abstract

PURPOSE:To rapidly produce the iron powder by solid reduction of iron oxides at a high reduction ratio without substantially melting the iron oxides by loading powdery iron oxide raw materials together with an excessive carbonaceous materials and carbonates into a vessel and projecting microwaves thereto. CONSTITUTION:The carbonaceous materials and the carbonates are compounded with the powdery iron oxide raw materials to prepare the refining materials. These materials are loaded into the vessel consisting of alumina, etc., and the vessel is loaded into an applicator. The loaded raw materials are then irradiated with the microwaves regulated to an extent of not melting the raw materials for a specific period of time to reduce the iron oxides to iron. The amt. of the carbonaceous materials to be compounded at that time is specified to >=2 times, more preferably about 4 to 6 times the equiv. (stoichiometric quantity complying with reaction formula = oxygen of oxidized iron + carbon = CO2) required for reduction of the iron oxides mentioned above. The carbonates are preferably CaCO3. The iron oxide raw materials consist preferably of hematite which is the essential component of Fe2O3 and consists essentially of the balance Fe2O3 or the raw material contg. the essential component of the Fe2O3 at >=40% ratio of the raw material are more preferable.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing iron powder using microwaves.

[0002]

2. Description of the Related Art Electromagnetic waves having a frequency of 1 to several hundred GHz
The microwave heating technology that heats the dielectric material by irradiating it with (microwave) is not only used in microwave ovens for cooking, but also industrially, rubber vulcanization equipment, drying equipment for various materials, thawing equipment,
It is widely used in the field of melting equipment.

A proposal to use this microwave heating for the reduction of metal oxides was made by Mr.
64-52028. The publication teaches that when a mixture of various oxide ores and a carbon source is charged into an applicator and irradiated with microwaves, the mixture is heated to a high temperature and a reduction reaction proceeds.

On the other hand, in the technique for producing iron powder by reducing powdery iron ore to iron in a solid state, iron ore and carbonaceous materials are loaded into a container as seen in Heganes iron powder and the like. There is a method of charging this in a tunnel furnace and externally heating it.

[0005]

[Problems to be Solved by the Invention] In the above-mentioned publication, Mr. Warner reported that the reduction of iron ore by microwaves resulted in the reduction of hematite (Fe ₂ O ₃ ) to magnetite (Fe ₃ O ₄ ). . In order to further reduce this magnetite to metallic iron, refining in a bath refining furnace is recommended (for example, Experimental Example 2 of the publication).

It is certain that the iron ore is mixed with a carbon source, and if the mixture is exposed to microwaves, the temperature rises. Since the carbon source (carbon such as coal and coke) absorbs microwaves well, it can be heated to a high temperature by the microwaves and the entire mixture can be heated to a temperature at which reduction proceeds. In addition, since Fe ₃ O ₄ generally absorbs microwaves well, it can be heated by microwaves, although not as much as carbon. However, Fe ₂ O ₃ is generally not heated.

On the other hand, in the production of iron powder (sponge iron) in a tunnel furnace, the efficiency of heat supply required for reduction of iron oxide is low, and a long reaction time and enormous heat supply are required.
There are problems in terms of energy efficiency and operational efficiency.

In view of such circumstances, the present invention further develops the microwave utilization technique proposed by Mr. Warner, and it is possible to perform microwave heating to metallic iron without substantially melting powdery iron oxide. The challenge was to establish a technology for solid reduction.

[0009]

According to the present invention, a refining material prepared by mixing powdery iron oxide raw material with carbonaceous material and carbonate is loaded into a container, and the material loading container is irradiated with microwaves. A method of reducing the iron oxide to iron by allowing it to stay in an applicator for a predetermined period of time, wherein the carbonaceous material is equivalent to the reduction of the iron oxide (oxygen of iron oxide + carbon = Provided is a method for producing iron powder using microwaves, which comprises blending in an amount of at least twice the stoichiometric amount according to the reaction formula of CO ₂ .

[0010]

[Function] When an excess amount of carbonaceous material is added to the refining material in excess of the equivalent amount required for iron oxide reduction, for example, as shown in Fig. 4 below, high reduction rate of iron oxide to iron is achieved by microwave heating. Can be reduced with. Properly adjusting the blending amount of the carbonaceous material plays an important role in increasing the reduction rate and the reduction rate. The preferable amount of the carbonaceous material is 2 times or more, preferably 4 times or more to 6 times the equivalent required to reduce the iron oxide.

When the carbonate is blended in the refining material, a higher reduction rate can be obtained within the same microwave irradiation time. This is because CO ₂ generated by thermal decomposition of carbonate is C
It is considered that this is because the CO concentration which is involved in the direct reduction reaction increases with the reaction. As shown in FIG. 5 described later, among carbonates, calcium carbonate has a large effect.

Fe ₃ O ₄ has a property of absorbing microwaves to generate heat, whereas Fe ₂ O ₃ has a weak property. Therefore, among iron ores, when using a hematite-based material containing Fe ₂ O ₃ as the main component, self-heating due to microwave heating cannot be expected. Therefore, when using hematite as an iron raw material, it is advantageous to mix Fe ₃ O ₄ raw material. When a compound containing Fe ₃ O ₄ as a main component (mill scale in the example) is mixed in an amount of 40% or more with respect to the total iron oxide, a high reduction rate that cannot be predicted only by the microwave absorbing property is obtained. Obtained (for example, FIG. 6 described later).

Char charcoal is advantageous as a carbonaceous material for obtaining a high reduction rate and a high reduction rate. Also, the smaller the particle size of the carbonaceous material, the higher the reduction rate and reduction rate obtained. When using coke, it is preferable to use one having a particle size of 150 μm or less.

When at least a part of the carbonaceous material is charged in a container so as to be separated from the iron oxide raw material in a layered state and subjected to a reduction treatment, the metal iron grade of the reduction product can be increased to 92% or more.

From the standpoint of producing iron powder, it is advantageous to control the reaction temperature so that melting is not caused by progressing reduction in a solid state from iron oxide to iron. This can be done by adjusting the microwave irradiation amount to the container loaded in the applicator. For example, an alumina cover or the like may be used to prevent the temperature from becoming excessively high. The refining vessel is preferably made of a refractory material such as alumina or silica through which microwaves can pass.

[0016]

EXAMPLES In the following experiments, a microwave oven with an output of 500 W and a frequency of 2.45 GHz was used as the microwave irradiation reduction apparatus. A magnetic plate having a thickness of 11 mm was placed on the bottom of the oven, a refining vessel was placed on the magnetic plate, and microwave irradiation was kept constant for 10 minutes unless otherwise specified. As the refining container, an alumina magnetic crucible having an inner volume of 30 ml was used. To measure the temperature, insert a magnetic tube through the hole drilled in the top of the oven, insert the magnetic tube to a position 7 mm from the bottom in the container, and attach the fiber tube to the bottom of the magnetic tube with a fiber-type radiation thermometer. The temperature was measured using.

The materials used for refining are as follows. [Powdered iron oxide raw material] Iron ore: Hematite with a grain size of -60 mesh from the Bailadila mine, India Mill scale: Grain size generated at a steel mill rolling mill -32 mesh
Iron oxide powder (Fe ₃ O ₄ ) [Carbon material] Char charcoal, Coke powder or Hongay coal [Carbonate] Limestone powder (CaCO ₃ ) with a grain size of −48mesh from the Adachi Mine

In each experiment, the sample after microwave irradiation has a high temperature and re-oxidizes if left as it is. Therefore, immediately after irradiation, N ₂ gas is blown into the sample to rapidly cool it, and after reaching the room temperature, the container ( After removing it from the crucible and separating it into magnetic and non-magnetic components with a hand magnet, the metallic iron in the magnetic component is chemically analyzed, and the metallic iron produced by reduction and the iron content in the iron oxide raw material are compared. The reduction rate was calculated as a percentage of the ratio.

[Example 1] In this example, the amount of char coal added to the hematite and the limestone was kept constant under the conditions of 10 g of hematite and 1 g of limestone, and the amount of char coal added was changed to three stages of 3 g, 5 g, and 10 g, and char char addition on the reduction rate of hematite was added. The effect of quantity was investigated. The results are shown in Fig. 1.

As is apparent from FIG. 1, the amount of char charcoal added
In the case of 3 g, an inverse S-shaped velocity curve due to the presence of the induction period is shown, and the reduction rate of hematite is small even when the steady state is reached. It is understood that this is because it takes time to raise the temperature of the reaction system that can trigger the reduction reaction of hematite. On the other hand, the induction period was not observed under the conditions of char coal amounts of 5 g and 10 g, and generally the reduction rate tended to increase as the char coal amount increased.

FIG. 2 is a graph in which the time required for 50% reduction from FIG. 1 is obtained, the average speed is calculated by the reciprocal thereof, and the average speed is plotted against the amount of char coal. As is clear from the results shown in FIG. 2, R ₅₀ increases almost linearly as the charcoal addition amount increases. The R ₅₀ becomes 0 when the amount of charcoal added is about 2.5 g or less, which means that 50% reduction of hematite cannot be achieved with the amount of charcoal added within this range.

On the other hand, FIG. 3 shows the rate of temperature rise of the char coal layer when only char char was loaded into the container, the container was covered with an alumina cover, and microwave heating was performed. As is clear from this figure, as the amount of char coal increases, the rate of temperature rise in the char coal bed and the maximum temperature reached tend to increase. This result shows the validity of the results of FIGS. 1 and 2.

[Example 2] As can be seen from the reduction rate curve of hematite in Fig. 1, under the conditions of the charcoal addition amounts of 5 g and 10 g, the reduction rate to metallic iron 10 minutes after the start of microwave irradiation The maximum return rate in Japan has reached close to 85%. Therefore, start microwave irradiation under certain conditions
It was fixed at (10 minutes), and this time, the effect of the charcoal addition amount on the metal iron grade of the reduction product 10 minutes after the start of the reduction reaction on the mill scale was investigated. At that time, the addition amount of mill scale was fixed at 10 g and the addition amount of limestone was fixed at 1 g, and the addition amount of char charcoal was changed. The results are shown in Fig. 4.

The lower horizontal axis of FIG. 4 shows the weight ratio of char charcoal to mill scale, and the upper horizontal axis shows the equivalent ratio of char charcoal to mill scale. The equivalent ratio is a reaction formula for reducing Fe ₃ O ₄ with C to produce CO ₂ (oxygen in Fe ₃ O ₄ + carbon =
It is an equivalent ratio based on CO ₂ ).

As is clear from the results shown in FIG. 4, as the equivalent ratio of char coal increases, the grade of metal iron in the reduction product sharply rises. When the equivalent ratio of char coal is around 1, the metal iron grade is less than 20%, and when the equivalence ratio is around 2, the metal iron grade exceeds 50%, and when the equivalence ratio is around 4, the metal iron grade is almost the same. There is a tendency to reach saturation.

That is, even if the carbonaceous material is blended in an equivalent amount required for the reduction of the iron oxide (a stoichiometric amount according to the reaction formula of iron oxide oxygen + carbon = CO ₂ ), the reduction to iron almost proceeds. Without
It is necessary for the reduction of iron oxides to metallic iron by microwave heating to mix carbonaceous materials in an amount of at least 2 times, preferably 3 times or more, more preferably 4 times or more in terms of equivalent ratio. Recognize. However, even if the carbonaceous material is blended in an equivalence ratio of more than 6, the metal iron grade cannot be so high by itself.

Example 3 In this example, the effect on the reduction rate of carbonate was investigated. Mill scale 6g + for iron oxide
Hematite 4g mixture, charcoal as charcoal (−16me
sh) 5 g, and as the carbonate, CaCO ₃ and MgCO ₃
-Mg (OH) ₂ was added to each 1 g. Further, a test in which these were not compounded and a test in which 1 g of CaO and MgO were compounded were also performed for comparison. The microwave irradiation time was constant for 10 minutes. The results are shown in Fig. 5.

As is apparent from FIG. 5, if carbonate is added at the same microwave heating time, a higher reduction rate can be obtained, and calcium carbonate has a great effect.

Example 4 In this example, hematite having Fe ₂ O ₃ as a main component and low microwave absorptivity and mill scale having Fe ₃ O ₄ as a main component and high microwave absorptivity were used as iron oxides. When used as raw materials, it was investigated whether or not there was an appropriate range for the mixing ratio of the two.

The test was carried out with iron oxide raw material = 10 g, limestone = 1
g, carbon material (char charcoal) = 5 g, the mixing ratio of mill scale and hematite in 10 g of iron oxide raw material was changed, and the microwave heating test similar to the above was conducted to examine the reduction rate.
The results are shown in Fig. 6.

As is apparent from FIG. 6, when the addition amount of the mill scale is 40% or less, the reduction behavior can be understood as the additivity of the mill scale and hematite. A reduction rate higher than expected from the formation was obtained. This phenomenon has good reproducibility.

That is, the reduction rate increases with the increase of the mill scale with good microwave absorption up to the addition amount of mill scale of 40%. An unexpectedly high reduction rate was obtained.

[Embodiment 5] This embodiment shows the results of tests conducted by changing the type of carbonaceous material. Char charcoal, coke powder, and hongay charcoal were selected as carbonaceous materials, and all were sized to -32 + 80mesh before use. A mixture of mill scale and hematite (weight ratio 60:40) was used as the iron oxide raw material. Mixing ratio of iron oxide raw material: carbonaceous material: limestone is 10 in any test.
g: 5g: 1g. FIG. 7 shows the relationship between the microwave irradiation time and the reduction rate when each carbon material was blended.

As can be seen from the results shown in FIG. 7, char charcoal is reduced extremely rapidly, and it has already been reduced to 75% by microwave irradiation for 5 minutes.
Although the reduction rate of 100% was reached, the reduction rate using coke was extremely low, and the reduction rate after 15 minutes of microwave irradiation was only 13%.

The reason why such a difference appears is not always clear. When observing the surface of each carbonaceous material in the SEM photograph, no significant difference is observed with the naked eye except that the surface of hongay charcoal shows extremely smoothness, and there is a large difference in volatile matter between char charcoal and coke. There is no significant difference in the fixed carbon content of the products. If we consider it as the effect of volatile matter, it cannot be explained that the reduction rate is low in the experiment using Hongay coal, which has almost the same volatile content as char coal.

Therefore, a microwave heating test was conducted only on each carbon material. The results are shown in Fig. 8. In the test, all the carbonaceous materials were sized to -32 + 80mesh, 10g was placed in each crucible, and the temperature was measured by microwave irradiation. The temperature rise is overwhelmingly fast. From the results, it can be considered that reduction using char charcoal showed the largest reduction rate as shown in Fig. 7, and that a high reduction rate was achieved.

On the other hand, as can be seen in FIG. 8, the rate of temperature rise of coke is second to that of char coal, but the maximum temperature reached is lower than that of Hongay coal, and the difference is between coke and Hongay coal. It is considered that this appears as a difference in the reduction rate in the case of the presence.

Example 6 In this example, the effect of the particle size of carbonaceous material on the reduction rate was investigated. Coke with different grain sizes was used as the carbonaceous material. A mixture of mill scale and hematite (weight ratio 60:40) was used as the oxide raw material, and the mixing ratio of iron oxide raw material: coke: limestone was used in all tests.
It is 10g: 5g: 1g. The relationship between the average particle size of coke and the reduction rate is shown in FIG.

As is clear from FIG. 9, even with the same coke, the reduction rate greatly increases as the grain size becomes finer, and if the average grain size is 150 μm or less, the reduction rate should be 50% or more. You can This is because the finer the coke, the better the contact between the iron ore and the coke.
It is considered that this is because the concentration of CO increases due to the decrease in the gap.

[Embodiment 7] In this embodiment, a carbonaceous material and an iron oxide raw material are separated and loaded into a container to carry out a reduction test.
In the test, 6 g of mill scale, 4 g of hematite, and 1.2 g of char charcoal (-16 mesh) were mixed into a first mixture, while 3.8 g of char charcoal and 1 g of limestone were mixed into a second mixture.
The first mixture was wrapped in paper and enclosed in a container such that it was surrounded by the second mixture. For comparison, a test was also conducted on a mixture of all the charges uniformly. Microwave irradiation time and metal iron grade of reduction products in each test
The relationship of (%) was investigated and the results shown in FIG. 10 were obtained.

As is clear from FIG. 10, in the mixed charging, even if the microwave irradiation time was lengthened, the metal iron grade in the reduction product reached only about 87%, but the separation charging was carried out. In this case, the quality of metal iron in the reduced product reaches 92%.

[0042]

As described above, according to the present invention,
The reduction proceeds from the iron oxide raw material to iron in a solid state, and the reduction reaction is extremely short and the reduction rate is high. Therefore, iron powder can be produced in high yield with high energy efficiency by using powdered iron oxide.

[Brief description of drawings]

FIG. 1 is a diagram showing the effect of the amount of charcoal added on the reduction rate of iron oxide.

FIG. 2 is a diagram showing the effect of the amount of charcoal added on the reduction rate of iron oxide.

FIG. 3 is a diagram showing a heating rate when only char charcoal is microwave-heated.

FIG. 4 is a diagram showing a relationship between an equivalent ratio of blended char coal and a metal iron grade of a reduction product.

FIG. 5 is a diagram showing the relationship between the type of carbonate and the reduction rate.

FIG. 6 is a diagram showing the effect of the mixing ratio of mill scale and hematite on the reduction rate.

FIG. 7 is a diagram showing the relationship between the type of carbonaceous material and the reduction rate.

FIG. 8 is a diagram showing the relationship between the type of carbonaceous material to be microwave-heated and the heating rate.

FIG. 9 is a diagram showing the relationship between the average particle size of coke and the reduction rate.

FIG. 10 is a diagram comparing the metal iron grades of the reduction products when the iron oxide and the carbonaceous material are separately charged and when they are mixedly charged.

Claims (6)

[Claims] 1. A container is charged with a refining material obtained by mixing powdery iron oxide raw material with carbonaceous material and carbonate, and the material loading container is placed in an applicator for which microwaves are projected for a predetermined time. A method for reducing the iron oxide to iron by allowing it to stay, wherein the carbonaceous material is equivalent to the reduction of the iron oxide (stoichiometric amount according to the reaction formula of iron oxide oxygen + carbon = CO ₂ ). (2) or more than twice the amount of the above). 2. The carbonate is calcium carbonate.
The method for producing iron powder using the microwave described in. 3. At least a part of the iron oxide raw material is
Hematite mainly composed of Fe ₂ O ₃ and the balance Fe ₃ O ₄
The method for producing iron powder using microwaves according to claim 1, which is a raw material containing as a main component. 4. The method for producing iron powder using microwaves according to claim 3, wherein the proportion of the raw material containing Fe ₃ O ₄ as a main component in the iron oxide raw material is 40% by weight or more. 5. The method for producing iron powder utilizing microwaves according to claim 1, wherein the carbonaceous material is charcoal in the form of fine powder or powder coke having an average particle size of 150 μm or less. 6. The container according to claim 1, wherein at least a part of the carbonaceous material is loaded into the container so as to be separated from the iron oxide raw material in layers.
Alternatively, the method for producing iron powder using microwave according to 2 above.