JPH1150165A - Recovery of zinc from iron-making dust - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently recover zinc from iron-making dust. SOLUTION: The iron-making dust 12 having 5 wt.% moisture, is added into molten iron 4 held in a vessel 2 under an inert gas atmosphere or under reduced pressure, and stirring gas is blown into the molten iron. Iron oxide and zinc oxide are reduced with carbon in the molten iron and the iron is recovered, and exhaust gas 22 containing vaporized zinc, is cooled to recover the zinc 30. At this time, the adding speed of the iron-making dust 12 into the molten iron 4 is preferably >=50 kg/min. Further, the stirring gas is preferably blown into >=1 m depth of the molten iron.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for returning iron contained in ironmaking dust (hereinafter simply referred to as dust) generated in an iron making process and a steelmaking process to an iron making process, reducing zinc oxide in the dust, The present invention relates to a method for concentrating and recovering the amount.

[0002]

2. Description of the Related Art Main ironmaking dust generated in an ironworks is blast furnace dry dust and blast furnace wet dust generated in an iron making process, and converter wet dust generated in a steelmaking process. Besides that,
There is electric furnace dust generated by electric furnace manufacturers. In both cases, blast furnace wet dust and converter wet dust are collected by a venturi scrubber and collected by a thickener. These wet dusts contain as much as 15 to 40% by weight of water, so that any subsequent treatment must be dried by a suitable means.

[0003] Table 1 shows the composition of components of the above-mentioned ironmaking dust other than moisture. Blast furnace dust is different in that it contains coke powder and therefore has a high carbon content, and converter dust contains much metallic iron. Blast furnace wet dust contains more zinc than other dust. As described above, zinc contained in various ironmaking raw materials such as ore and coal is concentrated in blast furnace dust, and when returned as blast furnace raw material, it concentrates in the blast furnace and damages the furnace wall refractories. The amount used is limited, and the following measures are generally taken.

[0004]

[Table 1]

[0005] Rotary kiln, shaft furnace, electric furnace,
Dezincing method using a dedicated furnace such as a smelting reduction furnace In this method, iron oxide dust is mixed with coal, coke, etc., heated by electricity or combustion of hydrocarbons, etc., and zinc oxide contained in a reducing atmosphere Is reduced and evaporated to recover zinc.

In this method, iron-making dust is extracted with an acid and zinc is precipitated as a hydroxide, or is extracted with ammonia and precipitated as a carbonate.

Method of recovering iron by adding ironmaking dust to hot metal in a blast furnace casting bed, hot metal pretreatment, or a converter as a substitute for mill scale, and recovering iron content In this method, oxygen gas is added to hot metal at 1300 to 1600 ° C. To collect iron in the ironmaking dust into the hot metal, and at the same time, reduce zinc oxide in the ironmaking dust.

[0008] Since the reduced zinc is vaporized and reattached to the dust generated at the same time, the dust is collected by a dust collector. The ironmaking dust volume is reduced to some extent depending on the conditions for adding the ironmaking dust to the hot metal, depending on the pretreatment of the hot metal in the cast floor gutter, ladle, etc. of the blast furnace and the addition to the converter. An example is shown in Table 2. As shown in Table 2, the increase in the zinc concentration in the iron-making dust is increased from 1.1 times to several times, and the volume of the iron-making dust is reduced, that is, the customer is reduced. .

[0009]

[Table 2]

[0010]

Although the dezincing rate is high in the prior art and the method, a dedicated dezincing furnace is required.
In general, there is no dedicated dezincing furnace in the existing steelworks, and the dezincing treatment is outsourced to a dezincing company. Therefore, at the same time as labor costs and transportation costs are incurred, the processing is performed at a high temperature of 1000 ° C. or more, so that the operation costs are high, and
There is a problem that the facility construction cost is extremely high.

Although the prior art method has greatly improved the processing cost in comparison with the prior art method, the main purpose is to use ironmaking dust as a substitute for mill scale and to recover the iron content in the dust. Therefore, as shown in Table 3, the dezincing efficiency of the collected dust, that is, the zinc concentration in the secondary dust is low, and the powder is not suitable as a zinc raw material. Furthermore, since the reduced zinc is oxidized during the cooling process,
Since it cannot be used directly as zinc, it must be reduced.

[0012]

[Table 3]

[0013] Accordingly, the present invention provides a method for directly returning iron-making dust generated in a pig-making and steel-making process to a pig-steel process, and simultaneously performing a dezincing treatment. Zinc concentration that can be supplied as about 40
It is an object of the present invention to provide a method for recovering zinc from iron-making dust that can be concentrated to wt% or more.

[0014]

Means for Solving the Problems As a result of various studies to solve the above-mentioned problems, the inventors have found that it is important to add iron-making dust to hot metal so that dust added to hot metal is not scattered as much as possible. It was found that.

Further, when ironmaking dust is added to the hot metal, iron is recovered in the hot metal. At this time, dust generated on the surface of the hot metal (secondary dust) is sucked by a dust collector or the like. Has found that zinc is concentrated, and when the exhaust gas containing the generated secondary dust is cooled by a gas cooler or the like, the zinc in the exhaust gas is deposited as metallic zinc because of its high vapor pressure. Reached.

A first invention is a method for recovering zinc from iron-making dust, comprising the following steps. (A) adding iron-making dust having a water content of 5 wt% or less to hot metal held in a container under an inert gas atmosphere or under reduced pressure;
(B) Agitating gas is blown into the hot metal to cause the hot metal and the ironmaking dust to react with each other, and (c) an exhaust gas containing secondary dust generated is cooled, and mainly metallic zinc is recovered.

If the ironmaking dust is a dust obtained by a wet dust collector, that is, a venturi scrubber, it usually contains moisture, so it is dried in advance to reduce the moisture to 5 wt% or less.
If necessary, ironmaking dust that has been crushed to a particle size of 2 mm or less is added to the surface of the hot metal held in a container such as a hot metal pot under an inert gas atmosphere or under reduced pressure.

Even if the dust is added to the hot metal at 1300 ° C. or more by reducing the water content in the ironmaking dust to 5 wt% or less, the generation of steam is small, and the yield of addition is good. The ironmaking dust reacts with the hot metal, the iron and zinc are efficiently reduced, and the secondary dust generated from the surface of the hot metal has a high zinc content, so that it can be recovered by cooling it. At this time, the reduced zinc is not reoxidized in an inert gas atmosphere. Further, when the pressure is reduced to, for example, 0.5 atm, the reduced zinc easily vaporizes due to a high vapor pressure and is hardly reoxidized.

A second aspect of the present invention is a method for recovering zinc from steelmaking dust, wherein the stirring gas is blown into the hot metal having a depth of 1 m or more when blowing the stirring gas into the hot metal. When using a lance to inject an inert gas as a stirring gas, if the lance is immersed in the hot metal at a depth of 1 m or more, when the stirring gas floats inside the hot metal, the hot metal is sufficiently stirred and the hot metal is stirred. Since the ironmaking dust on the hot metal surface is sufficiently reacted, the reduction reaction of the ironmaking dust is efficient, and the amount of secondary dust generated from the hot metal surface is reduced.

A third invention is a method for recovering zinc from ironmaking dust, wherein the rate of addition of the ironmaking dust to hot metal is in the range of 50 to 300 kg / min. If the rate of addition of the dust to the hot metal is less than 50 kg / min, the concentration of zinc in the secondary dust generated from the hot metal is undesirably low. The rate of addition of ironmaking dust to hot metal is 3
If it exceeds 00 kg / min, the scattering amount of iron-making dust is large, and the efficiency of addition is undesirably reduced.

A fourth aspect of the present invention is a method for recovering zinc from steelmaking dust, wherein the exhaust gas is cooled by a gas cooler. Since secondary dust generated from the surface of the hot metal has a high zinc content, high-purity metallic zinc can be recovered by cooling this exhaust gas with a gas cooler.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Ironmaking dust (hereinafter referred to as dust) mainly composed of iron oxide generated in an ironworks has the composition shown in Table 1. This component composition is a component composition from which moisture has been removed, and the wet dust directly obtained from the venturi scrubber contains 15 to 45% by weight of moisture.

Therefore, the water is first dried by various methods to make it at least 5 wt% or less. This is because when the dust is added to the surface of the hot metal, the moisture evaporates rapidly, and the dust is prevented from rapidly expanding and scattering. In addition,
There is also a method of blowing dust into the hot metal, but it is not preferable because water evaporates rapidly in the hot metal and the hot metal is scattered.

The particle size before drying is 1 mm or less, but when the particle size changes by drying, it is desirable to crush and reduce the particle size to 2 mm or less in order to maintain good reactivity. The above-mentioned dry dust does not usually need to be dried. This is because the water content is 5 wt% or less. Dust having a water content of 5 wt% or less can be transported by a carrier gas by a so-called dispenser and blown into hot metal in a hot metal pot through a lance, for example. Figure 1 shows the outline of the equipment.

As a container for storing the hot metal, a hot metal pot is sufficient, but a specially prepared container for dezincing may be used.
In FIG. 1, a lance 8 is immersed in hot metal 4 stored in a hot metal pot 2 as a container for storing hot metal, and dust 12 is added to the hot metal from a shot 10 while blowing an inert gas such as nitrogen gas as a stirring gas. I do.

The iron oxide in the dust is reduced by carbon contained in the hot metal to become Fe and CO gas, and Fe is recovered as iron. Further, ZnO in ironmaking dust is reduced to Zn and CO gas by carbon in hot metal. A small amount of unreacted dust and reduced zinc vapor are generated from the upper surface of the hot metal together with CO gas generated by the reduction of iron oxide.

The upper part of the hot metal ladle is sunk to prevent air from entering.
The exhaust gas 20 containing the generated secondary dust is sucked into the duct 14 and cooled in the gas cooler 16 provided with the water-cooled tube 18. The inside of the hood 6 is filled with an inert gas such as a nitrogen gas or an argon gas in order to prevent air from entering, so that evaporated zinc is not oxidized. Further, by evacuation by an appropriate evacuation means, the pressure in the hood is reduced to the atmospheric pressure or less, thereby promoting the evaporation of zinc and preventing the reoxidation of zinc.

Since the vapor of zinc contained in the exhaust gas is not reoxidized but adheres and adheres to the outer surface of the water-cooled tube 18, the metallic zinc 30 adhered by an appropriate means, for example, scraping means is collected. . Instead of the gas cooler 16, a conventional dust collector, for example, an electric dust collector, or a scrubber can be used. Other portions 22 in the exhaust gas are further discharged to the outside by a suction device (not shown).

[0029]

EXAMPLE The following describes the reaction situation when 220 tons of hot metal is placed in a hot metal pot, ironmaking dust is added and reduced. FIG. 2 shows the relationship between the dust addition rate, the amount of secondary dust generated, and the zinc concentration in this dust. In the present invention, since an inert gas such as nitrogen gas is used as the stirring gas, the amount of secondary dust generated is small, and the zinc concentration in the secondary dust increases with the addition rate. When the addition rate is 250 kg / min, zinc in the secondary dust generated is about 80 wt%.

FIG. 3 shows the effect of the immersion depth of the lance into which ironmaking dust is blown on the amount of secondary dust generated. When the lance immersion depth is 1 m or more, the reduction reaction is fast, the amount of secondary dust generated is small, and the reaction yield is high because the ironmaking dust added to the hot metal is sufficiently stirred.

The dust 12 can be blown by a dispenser (not shown) with a carrier gas such as nitrogen through a lance. FIG. 4 shows the relationship between the solid-gas ratio and the zinc concentration in the secondary dust when ironmaking dust is blown into the hot metal from the lance 8 at a predetermined solid-gas ratio. It has been shown that when steelmaking dust is blown from a lance, the influence of the solid-gas ratio is large.

Based on the above results, 220 ton of hot metal was charged into a 250 ton hot metal hot pot, a lance was immersed in the hot metal, and ironmaking dust was added to the hot metal under the conditions shown in Table 4.
Dezincification was achieved as shown in the figure. 1. 95% of zinc (dezincing rate) in the blown dust was recovered. 2. The amount of generated dust is 20 wt% of the amount of added dust.
And the ratio of the volume of dust to the volume of secondary dust (volume reduction ratio) was 1/5 or less. 3. The concentration of the recovered metallic zinc was 85% by weight.

[0033]

[Table 4]

[0034]

As described above, iron oxide dust is added to the surface of hot metal in an inert gas atmosphere or under reduced pressure, and an inert gas such as nitrogen is blown into the hot metal from a lance and stirred to reduce iron oxide from the iron-made dust. And not only can it be recovered as iron, but zinc can be recovered efficiently. At this time, if the secondary dust is cooled by a gas cooler, metallic zinc can be recovered. Therefore, zinc resources can be economically recovered, and the steel manufacturing process can be made more economical.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of equipment for implementing the present invention.

FIG. 2 is a graph showing the relationship between the addition speed of iron-making dust, the amount of secondary dust generated, and the zinc concentration in the dust.

FIG. 3 is a diagram showing the effect of the lance immersion depth on the amount of secondary dust generated.

FIG. 4 is a diagram showing the influence of the solid-gas ratio on the addition rate of a constant ironmaking dust.

[Explanation of symbols]

 2 Hot metal pot 4 Hot metal 6 Hood 8 Lance 10 Shut 12 Steelmaking dust 14 Duct 16 Gas cooler 18 Water-cooled tube 20 Exhaust gas containing secondary dust 22 Exhaust gas 30 Metal zinc

Claims (4)

[Claims] 1. A method for recovering zinc from iron-making dust, comprising the following steps: (A) adding iron-making dust having a water content of 5 wt% or less to hot metal held in a container under an inert gas atmosphere or under reduced pressure;
(B) Agitating gas is blown into the hot metal to cause the hot metal and the ironmaking dust to react with each other, and (c) an exhaust gas containing secondary dust generated is cooled, and mainly metallic zinc is recovered. 2. The method for recovering zinc from iron-making dust according to claim 1, wherein, at the time of blowing the stirring gas into the hot metal, the stirring gas is blown into the hot metal having a depth of 1 m or more. 3. The addition rate of the ironmaking dust is 50 kg /
The method for recovering zinc from iron-making dust according to claim 1 or 2, wherein the range is from min to 300 kg / min. 4. The method for recovering zinc from steelmaking dust according to claim 1, wherein said exhaust gas is cooled by a gas cooler.