JPH08193227A - Treatment of iron-making dust in indirect heating furnace - Google Patents

Abstract

PURPOSE: To provide a method for treating iron-making dust in which an iron and non-ferrous metal components such as zinc in the dust are separated and recovered more inexpensively than the conventional method by executing the reduction treatment at lower temp. than the conventional method, in zinc removing treatment in the iron-making dust. CONSTITUTION: In the reduction-treatment of the iron-making dust, after drying the iron-making dust, metallic aluminum-containing raw material being the reducing agent is mixed and this mixed material is charged into an outer heating type indirect heating furnace at 700-1000 deg.C under reducing atmosphere containing 20-100% hydrogen or carbon monoxide in the furnace and the oxides of iron, zinc, lead and cadmium are reduced and the non-ferrous metal components such as zinc are vaporized and removed from the dust. Thus, the reduction treatment of the dust can be executed at lower temp. than the conventional zinc removing method, and the iron together with the zinc can be recovered in high concns.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recycling process of iron-making dust generated in the iron-making industry. In an indirect heating furnace in a reducing atmosphere, metal oxides are reduced and volatilized to remove iron and non-ferrous components. The present invention relates to a processing method for collecting.

[0002]

2. Description of the Related Art The dust generated in the steel industry includes blast furnace dust generated from a blast furnace, converter dust generated from a converter, electric furnace dust generated from an electric furnace, and the like. The main component of these is iron oxide, which can be expected to be reused in the iron-making process. However, dust contains non-ferrous metal components such as zinc in addition to iron, and dust cannot be recycled. It is necessary to separate and recover the iron and non-iron components in the dust.

Conventionally, as a known technique for treating iron-making dust containing such non-ferrous metal components, Japanese Patent Laid-Open No. 58-141 has been proposed.
As disclosed in Japanese Patent No. 345, by subjecting iron-making dust to heat treatment at 1000 ° C. to 1400 ° C. in an internal combustion type rotary kiln together with carbonaceous materials such as coal and coke, non-ferrous metal components such as zinc are reduced and volatilized and removed from the dust. However, the volatile component is generally reoxidized on the outlet side of the furnace and then recovered as an oxide by a bag filter.

Here, as the reducing agent, there is a method of using metallic aluminum in refined aluminum ash in addition to carbonaceous materials such as coal and coke. Further, in JP-A-60-162736, an internal combustion type rotary kiln is disclosed in JP-A-05-
Japanese Patent No. 320779 discloses a method of using metal aluminum in aluminum refined ash as a reducing agent for ironmaking dust in a vertical reduction melting furnace.

[0005]

However, in the method of reducing iron-made dust with carbonaceous material, the treatment temperature is as high as 1000 ° C. or higher, and therefore the maintenance cost of heat-resistant equipment and the unit quantity of heat are high. On the other hand, in the method of using metallic aluminum as a reducing agent, the heavy metal component contained in the dust can be reduced at a relatively low temperature of 1000 ° C. or lower. However, in the conventional reduction furnace, the combustion flame as a heating source is present in the furnace, and therefore oxygen in the atmosphere for combustion and steam and carbon dioxide produced by the combustion are present in the furnace. These gases oxidize metallic aluminum according to the following reaction formula.

[0006]

[Equation 1]

For this reason, metal aluminum that contributes to the reduction of ironmaking dust is deficient, and eventually the deficient reducing agent is supplemented with carbonaceous material that is being fed as a heat source fuel in the furnace, and high-temperature treatment at 1000 ° C. or higher. Therefore, the basic unit of calorific value is not reduced so much. Further, in the conventional method using the internal combustion type rotary kiln, the reduced and volatilized non-ferrous metal component such as zinc is reoxidized on the outlet side of the furnace and then recovered by a bag filter as fine dust, and the zinc concentration of the recovered dust is
It remains around 50-60%. Therefore, the recovered material containing zinc as a main component must be further reduced and refined in a non-ferrous smelting plant.

[0008] Therefore, an object of the present invention is to provide a treatment method capable of reducing iron-making dust by low-temperature treatment at low cost and separating and recovering high-purity iron and non-ferrous components.

[0009]

Means for Solving the Problems The present invention is to solve the above-mentioned problems, and its gist is to: (1) In the reduction treatment of iron-making dust, after the iron-making dust is dried, a metal as a reducing agent is used. External heating indirect heating at a furnace temperature of 700 to 1000 ° C. with a mixture of an aluminum-containing raw material containing aluminum and a furnace atmosphere of a reducing atmosphere containing 20% to 100% of hydrogen or carbon monoxide. A method for treating iron-making dust, which comprises charging the mixture into a furnace, reducing oxides of iron, zinc, lead, and cadmium in the dust, and volatilizing and removing zinc, lead, and cadmium from the dust.

(2) In the mixture of the iron-making dust and the aluminum-containing raw material, the mixture is made into pellets having a particle diameter of 2 to 15 mmφ (1) The method for treating the iron-making dust (3) The zinc, lead and cadmium The method for treating iron-making dust according to (1), wherein after removing the metal volatile component from the exhaust gas containing the metal volatile component, the exhaust gas is recovered and reused as the atmosphere gas in the furnace.

(4) After removing the metal volatile components from the exhaust gas containing the metal volatile components of zinc, lead and cadmium, the exhaust gas is recovered and reused as the heating fuel for the indirect heating furnace. (1) The method for treating iron-making dust described in (1). In the present invention, as the aluminum-containing raw material, for example, aluminum can scrap, aluminum refining dross, aluminum refining dust ash, aluminum refining residual ash, etc. can be used. The content of metallic aluminum in aluminum can waste is 95% or more, and in aluminum refining dross is 35% or more.
%, About 10% for aluminum refined dust ash and aluminum refined residual ash.

[0012]

The operation of the present invention will be described below. The overall process flow for implementing the invention is shown in FIG. In addition, in FIG. 1, a solid processing flow is shown by a solid line, and a gas flow is shown by a dotted line. In the present invention, in order to avoid the oxidation reaction of the metallic aluminum contained in the aluminum-containing raw material with atmospheric oxygen for combustion, and steam and carbon dioxide produced by combustion (the aforementioned chemical reactions (1) to (3)). An externally heated indirect heating furnace that separates a combustion flame atmosphere as a heating source and a reaction atmosphere for reducing dust is used as a reduction furnace.

By this, from the reaction atmosphere in the furnace,
Oxygen in the atmosphere for combustion, water vapor and carbon dioxide produced by combustion can be eliminated, and oxidation of metallic aluminum by these gases can be prevented. The indirect heating furnace of the present invention preferably uses an externally heated rotary kiln capable of stirring and transporting the treatment material in the furnace. Further, the ironmaking dust needs to be dried before being mixed with the aluminum-containing raw material. This is because if ironmaking dust is mixed with an aluminum-containing raw material without drying, the aluminum nitride contained in the aluminum-containing raw material may react with water to generate ammonia gas that is toxic to the human body. This is because the moisture reacts with metallic aluminum in the heating furnace, and the reaction efficiency of metallic aluminum as a reducing agent decreases.

Furthermore, it is important to mix the ironmaking dust and the aluminum-containing raw material evenly. Usually, aluminum smelting dross, dust collecting ash, and residual ash are powders, so when mixing with iron-making dust, it can be stirred and mixed without any problems, but in the case of aluminum can scrap, it is necessary to shredder it. It is desirable to use aluminum refining dross, dust ash, and residual ash as the raw material. Further, when using an external heat type rotary kiln, in order to prevent the produced reduced iron from adhering to the furnace wall of the rotary kiln by reducing the iron-making dust, a mixture of iron-making dust and aluminum smelting ash is pelletized. It is advantageous to leave it. If the particle size of this pellet is less than 2 mmφ, the pellet is likely to be crushed and pulverized in the furnace, causing a problem of dust adhesion to the furnace wall, and if it exceeds 15 mmφ, reduction of non-ferrous metal components such as zinc inside the pellet. Since the effect of suppressing volatilization becomes large,
2 to 15 mmφ is preferable.

Further, the mixing ratio of the iron-making dust and the aluminum-containing raw material varies depending on the amount of oxides of iron, zinc, lead, etc. in the dust and the content of metallic aluminum in the aluminum refined ash. Basically, it is necessary to use metallic aluminum that corresponds to the reduction of the oxides in the dust that is the object of reduction, but it is necessary because metallic aluminum reacts with water vapor or carbon dioxide that is present in a small amount in the reducing atmosphere. Mix with an aluminum-containing raw material containing metallic aluminum equivalent to 1.2 to 1.3 times the equivalent weight.

For example, when the composition in the dust is as shown in Table 1 and the composition of the aluminum smelting dust ash is as shown in Table 2, iron, zinc and lead in the dust are The amount of metallic aluminum required to reduce all to metal is 200 g / kg-dust, so in the case of aluminum smelting dust ash as shown in Table 2, it will be mixed at 2 kg / kg-dust.

[0017]

[Table 1]

[0018]

[Table 2]

In the present invention, a gas containing hydrogen or carbon monoxide is used as the atmosphere gas in the furnace. Examples of the gas source include coke oven gas (COG gas), converter gas, hydrocarbon partial combustion gas, Alternatively, a mixed gas of these can be used. Table 3 shows a coke oven gas composition example, Table 4 shows a converter gas composition example, and Table 5 shows a propane partial combustion gas composition example.

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

[Table 5]

In this case, if the concentration of hydrogen or carbon monoxide is less than 20%, the reaction rate becomes slow and it is not effective. Therefore, the concentration of the atmosphere in the furnace is adjusted to 20% or more. Also,
Since hydrogen is more effective than carbon monoxide in increasing the reaction rate, it is desirable to use a coke oven gas having a hydrogen concentration of 50 to 65% and being relatively inexpensive.

As the reaction mechanism in the present invention, since the melting point of metallic aluminum is 660 ° C., the metallic aluminum liquefied in the furnace comes into contact with the oxide in the dust to cause the following reduction reaction.

[0025]

[Equation 2]

In this reaction, zinc, lead and cadmium other than iron volatilize as metal vapor and are separated from the solid content. Also,
Since the furnace atmosphere is a reducing atmosphere containing hydrogen or carbon monoxide, the oxides in the dust are also reduced by these reducing gases.

[0027]

(Equation 3)

However, since the water vapor or carbon monoxide generated by this reaction and metallic aluminum cause the reaction of the above-mentioned reaction formula (2) or (3), the reaction formula (4) is apparently obtained. The reaction of (8) will be performed. Therefore, hydrogen or carbon monoxide in the atmosphere in the furnace has an effect of apparently reacting with the metal aluminum and the oxide not in direct contact with the metal aluminum.

In the present invention, this furnace temperature is 700 ° C. (zinc vapor pressure at 700 ° C. is 0.0) as the temperature at which metallic aluminum begins to melt and zinc and cadmium start to volatilize.
8 atm) or higher. The furnace temperature is 1000 ° C
If it exceeds, the unit quantity of heat for external heating of the indirect heating furnace becomes high, and moreover, SUS used as the material of the indirect heating furnace
Since stainless steel materials such as 310S approach the limit of use, it is necessary to set the temperature to 1000 ° C or lower. Since the reduction reaction of zinc oxide with hydrogen sharply increases over 800 to 900 ° C, it is particularly preferable to carry out the reduction treatment at 800 to 950 ° C.

Regarding the concentration of metal volatile components in the exhaust gas, since the contents of water vapor and carbon dioxide in the exhaust gas are small, the metal volatile components are oxidized by these gases ((9) to (18 (Reverse reaction of)) is less affected and can be concentrated to near saturated vapor pressure. For example, the exhaust gas temperature is 7
At 00 ° C., the saturated zinc vapor concentration at 700 ° C. and 1 atm is 8%, so the zinc vapor concentration in the indirect heating furnace can be set to 8% or less. The setting of the metal vapor concentration can be adjusted by the amount of the atmosphere gas charged into the indirect heating furnace with respect to the content of the volatile metal component in the dust. For example, if the dust to be treated has the composition shown in Table 1 and the zinc vapor concentration in the exhaust gas is set to 8%, 0.5 Nm ³ / kg-
It is only necessary to add the atmospheric gas of dust. The metal volatile components concentrated in the exhaust gas to near the saturated vapor pressure can be condensed and liquefied and recovered by cooling the exhaust gas.

The composition of the exhaust gas from which the metal volatile components have been removed is almost the same as the gas component at the time of charging into the indirect heating furnace, so that it can be circulated and used as a reducing atmosphere gas. However, the gas contains a small amount of water vapor, carbon dioxide, and ammonia generated from aluminum nitride in aluminum smelting residual ash, so it is necessary to circulate the gas several times before removing the ammonia. There is. The exhaust gas can also be used as heating fuel for an indirect heating furnace.

The solid content after the reduction treatment contains reduced iron and can be used as an iron source. However, since a large amount of oxides such as aluminum oxide are contained in addition to iron, the solids are crushed, and then magnetic separation is performed to separate iron-based magnetic substances and non-magnetic substances. As a non-magnetic material, it is recovered as a roadbed material and a cement raw material. Hereinafter, the present invention will be described in more detail based on examples.

[0033]

Example 10 kg of electric furnace dust having the composition shown in Table 1 was subjected to reduction volatilization treatment under various conditions. The treatment conditions are: heat treatment in a nitrogen atmosphere with an aluminum-containing material added; treatment conditions: heat treatment in an atmosphere equivalent to coke oven gas without adding an aluminum-containing material; treatment conditions include an aluminum-containing raw material; equivalent to a coke oven gas Heat treated in an atmosphere.

As the aluminum-containing raw material, 20 kg of aluminum refined dust ash having the composition shown in Table 2 corresponding to the reduction equivalent of electric furnace dust was used. An external heating type electric furnace is used as the heat treatment device, and the atmosphere gas having a composition (H ₂ / CH ₄ / N ₂ = 55/35/10) is circulated at 0.3 l / min as the coke oven gas equivalent atmosphere, It was treated at 800 ° C. for 60 minutes. Table 6 shows the results.

[0035]

[Table 6]

It can be seen that it is difficult to reduce and volatilize zinc and lead at 800 ° C. when only the aluminum-containing raw material is used as the reducing agent under the processing conditions shown in Table 6. On the other hand, in the reducing atmosphere, the dezincification rate was 41.8% when the processing conditions did not include the aluminum-containing raw material.
When the aluminum-containing raw material was added under the treatment conditions, the zinc removal rate was 92.4% and the lead removal rate was 70.0%, which was a dramatic improvement.

Further, it was found that the hydrogen concentration in the atmosphere gas on the outlet side of the furnace under the processing conditions was 54.0%, which was almost the same as the composition of the input gas and could be circulated and used as the atmosphere gas. Furthermore, in the processing conditions, after mixing the electric furnace dust and the aluminum refined dust collecting ash into pellets of 10 mmφ, as a result of heat treatment in a coke oven equivalent atmosphere, reduced iron does not adhere to the wall surface of the rotary kiln, and the same as above. The dezincification rate was 90% or higher, and the lead removal rate was 70% or higher.

[0038]

EFFECTS OF THE INVENTION As is clear from the above examples, according to the present invention, an aluminum-containing raw material is added to iron-making dust, and a metal component in the dust is reduced and volatilized in a reducing atmosphere furnace. It is possible to remove zinc from iron-making dust at low temperature and recover iron and zinc with high purity.

[Brief description of drawings]

FIG. 1 is a process flow diagram of solids and gases in iron dust processing according to the present invention.

Claims (4)

[Claims] 1. In the reduction treatment of iron-making dust, after drying the iron-making dust, a mixture with an aluminum-containing raw material containing metallic aluminum as a reducing agent is used, and the atmosphere in the furnace contains hydrogen or carbon monoxide of 20% to 100%. % In a reducing atmosphere, the temperature in the furnace is 700 to 1000 ° C., and the mixture is put into an externally heated indirect heating furnace, and iron, zinc in dust,
A method for treating iron-making dust, which comprises reducing oxides of lead and cadmium and volatilizing and removing zinc, lead and cadmium from the dust. 2. The method for treating iron-making dust according to claim 1, wherein the mixture of the iron-making dust and the aluminum-containing raw material is formed into pellets having a particle diameter of 2 to 15 mmφ. 3. After removing the metal volatile components from the exhaust gas containing the metal volatile components of zinc, lead and cadmium,
The method for treating iron-made dust according to claim 1, wherein the exhaust gas is recovered and reused as the atmosphere gas in the furnace. 4. After removing metal volatile components from the exhaust gas containing the metal volatile components of zinc, lead and cadmium,
The method for treating iron-making dust according to claim 1, wherein the exhaust gas is recovered and the exhaust gas is reused as heating fuel for an indirect heating furnace.