JPH07173548A - Method for recovering zinc from zinc-containing dust - Google Patents

Abstract

PURPOSE:To recover the valuable metal consisting essentially of zinc contained in dust in a pure form by keeping the top of a vertical smelting reduction furnace at a specified temp. while zinc-contg. dust is blown into the furnace. CONSTITUTION:The zinc-contg. dust mixed with limestone, quartzite, etc., is blown into a smelting reduction furnace 1 by a blowing device 15, reduced to form zinc vapor, passed through a carbonaceous material-packed bed (c), discharged from a duct at the furnace top and recovered by a cooler 7. The iron oxide in the dust and the oxides of Cr, Cd, etc., are melted in the raceway at the tip of a tuyere and descends toward a lower tuyere 2b. The descending melt is brought into contact with reducing gas produced at the tip of the tuyere 2b, reduced and separated into metal and slag. Cr, Cd, etc., are fixed in the metal or the slag and made harmless. While the zinc-contg. dust is blown into the furnace 1, the top of the furnace 1 is kept at >=600 deg.C by the combustion of the waste gas using the lances 12a and 12b for the secondary combustion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is intended to efficiently recover zinc from zinc-containing dust generated in an electric furnace or the like.

[0002]

2. Description of the Related Art In recent years, recycling of iron scrap has been desired from the viewpoint of resource recycling and energy saving. However, the quality of iron scrap varies greatly depending on the source.

For example, almost all self-generated scraps (iron scraps generated in the steel manufacturing process) have a clear identity and a small amount of impurities mixed therein, so most of them are consumed in the generation plant. On the other hand, secondary processing scraps and old scraps are those that include a large amount of scraps of surface-treated steel plates and special steels, because they are collected after the secondary processing of steel products and the final products have been incorporated and then collected separately. , These are refined and reused in the electric furnace maker.

In the electric furnace dust generated at that time, several percent of elements such as chromium, cadmium, lead, etc., which elute when the landfill is disposed and cause environmental pollution, and Zn content corresponding to the impurity of the raw materials, are contained. Is 20-40%, and iron is 25-50
% Or more, it has been strongly desired to treat and recycle these, that is, to fix toxic metals such as chromium, cadmium and lead at a low cost and to recover and recycle valuable metals such as Zn and Fe. .

As a prior art related to this point, for example, in Japanese Patent Laid-Open No. Sho 64-90081, electric furnace dust is agglomerated, and the agglomerated electric furnace dust is added and mixed in a molten steelmaking slag together with a reducing agent. A method has been proposed in which a valuable metal compound mainly composed of Zn which is melted and volatilized by oxygen gas bubbling is recovered and a harmful element is fixed in slag. In addition, Japanese Patent Laid-Open No. 2-38535 discloses that electric furnace dust is
It is supplied to a gas-sealed electric furnace together with a reducing agent and a melting agent,
A method of recovering volatile metals in the form of dust and valuable metals such as Fe in the form of molten metal is further disclosed in
Japanese Patent Laid-Open No. 5-65552 discloses, as a novel electric furnace dust treatment method, a flash reactor type melting treatment furnace using a burner composed of oxygen-based auxiliary gas and fuel injection.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the method disclosed in Japanese Patent Laid-Open Publication No. 2008-242242, it is necessary to additionally add a step of agglomerating the electric furnace dust, and there is a problem in that it is difficult to recover and recycle valuable metals such as Fe.

Further, in the method disclosed in JP-A-2-38535, since a raw material having a low content ratio of valuable metals is steel-made using an electric furnace, the method disclosed in JP-A-5-65552 is further disclosed. Since it is necessary to use a large amount of oxygen, all of them were expensive treatment and recovery methods.

The object of the present invention is to prevent the agglomeration of dust from being contained in dust such as electric furnace dust, in particular, volatile valuable metal mainly composed of zinc without increasing the cost. , Use as little electric energy as possible, recover and reuse non-volatile valuable metals contained in dust, and achieve the fixation of environmentally harmful metals such as chromium, cadmium, and lead) in the purest form possible We are proposing a new method that can be recovered.

[0009]

According to the present invention, zinc-containing dust such as electric furnace dust is blown through tuyere into a vertical smelting reduction furnace having a packed bed of a carbon-based solid reducing agent, and zinc in the dust is injected. While recovering zinc while reducing and evaporating the components, and cooling the exhaust gas containing this vaporized zinc vapor outside the furnace, the temperature at the top of the vertical smelting reduction furnace is maintained during the blowing of zinc-containing dust. Is a method of recovering zinc from zinc-containing dust, characterized in that

In the above method, the top temperature of the vertical smelting reduction furnace is preferably adjusted by a plurality of combustion lances for secondary combustion of the exhaust gas generated in the furnace.
It is preferable that all or part of the dust generated in the vertical smelting reduction furnace is blown into the vertical smelting reduction furnace again through the tuyere.

[0011]

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the configuration of equipment suitable for carrying out the present invention. In the figure, 1 is a vertical smelting reduction furnace having a bed c filled with a carbon-based solid reducing agent, 2a,
Reference numeral 2b denotes a tuyere (in this example, it is shown as having two upper and lower stages) provided in the vertical smelting reduction furnace 1. The tuyere 2a, 2b is provided with a hot air generator through a pipe line 3. 4 is connected.

Reference numeral 5 is a blower capable of sending air or oxygen as required to the hot air generator 4 through a pipe 5a, 6 is a hopper for carbonaceous material, and 7 is gas discharged from the vertical melting and reduction furnace 1. An exhaust gas cooling device for cooling a
The exhaust gas cooling device 7 includes a cooling tower 7a, a cooling water pipe 7b, and a pump 7c.

Further, 8 is a cyclone connected to the gas cooling device 7, 9 is a bag filter arranged behind the cyclone 8, and 10a and 10b are cyclones 8 and bag filters 9.
The hoppers 12a and 12b for feeding the dust (metal zinc or zinc oxide) collected in the transportation device 11 to the transportation device 11 are secondary combustion lances arranged in the upper part of the smelting reduction furnace 1. The lances 12a and 12b for the furnace are the furnaces of the vertical smelting reduction furnace 1 in which oxygen or air is blown by opening and closing the valves V ₁ and V ₂ (flow rate regulator) according to the instruction from the controller 14 according to the measurement result of the thermometer 13. Adjust the temperature at the top to be the proper temperature. Further, 15 is a powder blowing device which cuts out an appropriate amount of zinc-containing dust (electric furnace dust, etc.) and blows it into the smelting reduction furnace 1, and is added here for the purpose of adjusting the viscosity of the slag and the liquidus temperature. The smelting solvent is mixed in a predetermined ratio.

In the vertical smelting reduction furnace 1, there is a carbon material filling layer c.
Is formed, and the carbonaceous material is supplied by the hopper 6 so as to form a predetermined stock line at the top of the reduction furnace 1.

Blower air (may contain an appropriate amount of oxygen)
Is sent to the hot air generator 4 by the blower 5 800 ~
After being heated to 1000 ° C., hot air is blown into the smelting reduction furnace 1 from the tuyere 2a and 2b through the pipe 3, thereby burning the carbonaceous material.

Zinc-containing dust (electric furnace dust, etc.) is mixed in a predetermined ratio with a smelting solvent for limestone and silica stone, which is added in advance for the purpose of adjusting viscosity and liquidus temperature of slag, and a powder blowing device is used. After being blown into the smelting reduction furnace 1 by 15, it is reduced by the combustion heat of the carbonaceous material and the reducing gas to become zinc vapor, which is discharged from the duct at the top of the furnace through the filling layer c of the carbonaceous material.

Iron oxide in zinc-containing dust is chromium,
Together with other oxides such as cadmium, they are melted in the tuyere raceway by the combustion heat of the carbonaceous material and descend toward the tuyere 2b in the lower stage. And this descending melt is the tuyere 2b.
It is reduced by contacting with the high-temperature reducing gas generated at the tip of the plate in an alternating current, and is also directly reduced by contact with the packed layer c during the dropping and is separated into metal and slag. At this time, the reduction reaction heat, which is an endothermic reaction, is supplemented by the high-temperature reducing gas generated at the tip of the tuyere 2b.

The molten metal accumulated at the bottom of the vertical smelting reduction furnace 1 is discharged from the tap 1a, and the slag is discharged from the slag 1b. Chromium, cadmium, etc. are also fixed in the molten metal or slag. Will be rendered harmless.

In the present invention, the temperature of the top of the vertical smelting reduction furnace is kept at 600 ° C. while the dust containing zinc is being blown.
The above is held, and the reason will be described below.

In the treatment of electric furnace dust using a carbon material packed bed type smelting reduction furnace, since the electric furnace dust contains a large amount of oxides of volatile elements such as zinc oxide, it is difficult to prevent ventilation. Frequent operating problems such as hanging the racks cause unstable operation in the smelting reduction furnace.

As a result of conducting various kinds of experiments and examinations in order to investigate such a cause, the following has become clear.

(1) When air flow obstruction or hanging is generated, a large amount of deposits mainly composed of a mixture of ZnO and C is observed on the surface of the carbonaceous material in the upper part of the furnace and the wall surface of the furnace top. (2) Ventilation obstruction and hanging will always occur when the furnace top temperature is low. (3) When the furnace top temperature is low, ZnO is more stable than Zn vapor even in the packed bed of carbonaceous material, which is estimated to have high reducibility. (4) Furnace top temperature and oxidization degree of furnace top gas ((CO ₂ + H ₂ O) / (CO + CO ₂ + H ₂ + H ₂ O)) when the furnace top temperature is low, presence of Zn in the furnace top gas The morphology (Zn vapor or ZnO) was as shown in Figure 2. (5) The Zn vapor pressure of the furnace top gas changes according to the zinc content of the electric furnace dust, but in the operating range possible by the method of the present invention, measurement by a furnace top mass spectrometer or rapid aggregation of the sampled gas From the chemical analysis value of the aggregates collected and the value estimated from the amount of collected gas, it became clear that it was about 0.01 to 0.1 atm. (6) From the above, in the operation of a vertical smelting reduction furnace (with a two-stage tuyeres), Zn vapor is used as the form of Zn in the furnace top gas, and operation troubles such as ventilation obstruction and hanging are suspended. In order to operate the smelting reduction furnace stably without causing it, it is necessary to set the furnace top temperature to 600 ° C or higher.

Here, in the operation of a vertical smelting reduction furnace having a normal two-stage tuyere as shown in FIG. 1 above, even if it is attempted to maintain the furnace top temperature at 600 ° C. or higher, it should be lower than that. There is. Therefore, in the present invention, the exhaust gas is burned by using the secondary combustion lances 12a, 12b provided on the furnace top.

If the exhaust gas is burned by using the secondary combustion lances 12a, 12b, the Zn existing form in the furnace top gas becomes Zn vapor, and operation troubles such as ventilation obstruction and rack hanging are caused. A stable operation can be performed without causing it.

The furnace top temperature that must be achieved by the secondary combustion is preferably determined according to the furnace top temperature before the secondary combustion and the partial pressure of Zn vapor in the furnace top gas, for example, according to the conditions shown in FIG. .

For example, the furnace top temperature before the secondary combustion is 500 ° C.
When the oxidization degree of the furnace top gas is 0.8 and the partial pressure of Zn vapor in the furnace top gas at that time is 0.1 atm, as shown in Fig. 3, the oxidization degree increases due to the secondary combustion. In consideration of the effect of this and the effect of increasing the furnace top temperature, the furnace top temperature after secondary combustion is 1000 ° C or higher.

It is not a good idea to raise the temperature at the top of the furnace blindly because it will cause damage to the refractory. Therefore, it is preferable to adjust the temperature so as to obtain an appropriate furnace top temperature as shown in FIG. 3 above, taking into consideration the Zn vapor partial pressure measured by a mass spectrometer and the like as well as the temperature measurement result at the furnace top. . Regarding the temperature of the furnace top, it can be said that an appropriate temperature is 1200 ° C or lower.

In the equipment having the configuration shown in FIG. 1 above, the exhaust gas discharged from the smelting reduction furnace 1 is cooled by the cooling device 7, but this is contained in the exhaust gas. Zn vapor or Zn oxide are fine particles with a particle size of 3 μm or less, and they become pseudo particles and are extremely fine particles of 5 to 10 μm. Therefore, it is not possible to use a fine dust collection duster such as a tap filter as it is. It will be difficult. Fig. 4 shows an example of the structure of the equipment without the secondary combustion lance.

Next, as an embodiment of the present invention, all or part of the dust generated in the furnace is blown into the furnace again through the tuyere provided in the furnace. The blowing of this dust will be described below.

In the present invention, the zinc oxide in the electric furnace dust blown from the upper tuyeres as described above is used.
ZnO is reduced to Zn vapor and discharged from the furnace top through the packed bed of carbon-based solid reducing agent, but there is room for improvement in the following points.

That is, (1) In addition to Zn, a large amount of carbon and ash of coke, which is a carbon-based solid reducing agent, is mixed in the exhaust gas of the vertical smelting reduction furnace, so that the concentration of Zn in the dust is relatively high. The decline is inevitable. (2) A small amount of Fe is also contained in the dust ejected from the vertical smelting reduction furnace, so that the amount of metal recovered, that is, the decrease in productivity, cannot be avoided. (3) When the amount of fine carbon powder that jumps out of the vertical smelting reduction furnace increases, the carbonaceous material unit increases, which inevitably increases the manufacturing cost.

The present invention blows all or a part of the dust generated in the melting vertical reduction furnace through the tuyere into the furnace again so that the volatile valuable metal mainly containing Zn is in a pure form. It is extremely advantageous not only to recover the carbonaceous material in the above-mentioned manner, but also to reuse the carbonaceous material in the dust and in addition to recover the low boiling point valuable metals such as Fe in the dust with a high yield for recycling.

FIG. 5 shows the configuration of equipment suitable for blowing at least a part of the dust generated in the furnace through the tuyere into the furnace again.

In order to make the Zn concentration higher and to effectively utilize the carbon in the recovered dust, a dust collector such as a cyclone 16 is installed at the rear stage of the vertical smelting reduction furnace 1 and the cooling device 7 as shown in FIG. It is effective to place it in the previous stage.

First, when the cooling device 7 is arranged directly on the outlet side of the vertical smelting reduction furnace 1 without installing the cyclone 16, the Zn vapor discharged from the top of the reduction furnace 1 is again cooled by the cooling device 7.
Although recovered as ZnO, the dust thus obtained (hereinafter referred to as recovered dust) contains a large amount of carbon derived from carbonaceous material.

On the other hand, when the cyclone 16 is installed between the vertical smelting reduction furnace 1 and the cooling device 7, the dust, which mainly consists of Zn and which contains carbon and ash, is ejected from the vertical smelting reduction furnace 1. Of these, the dust containing carbon particles of about 10 μm or more, which is generated from carbonaceous material, is collected by the cyclone 16 and most of the carbon components contained in the dust can be separated, and the cooling device 7 and the bag filter 9 are separated. hand
The Zn content will be recovered. Therefore, (1) By separating the carbon content, the Zn concentration in the recovered material in the cooling device or the bag filter can be improved. (2) The carbon content recovered by the cyclone can be recycled, which is effective in reducing the carbonaceous material unit of the vertical smelting reduction furnace. (3) Since metal components such as Fe contained in the dust collected by the cyclone can be recycled, it is possible to avoid a decrease in metal productivity.

On the other hand, when the cooling device 7 is provided on the outlet side of the vertical smelting reduction furnace 1 and the cyclone 16 is arranged in the subsequent stage, most of the carbon component due to carbonaceous material is deposited on the cooling device 7. Therefore, it is appropriate to dispose a dust collector such as the cyclone 16 in the latter stage of the vertical smelting reduction furnace 1 and in the former stage of the cooling device 7.

The dust collected by the cyclone 16 (the dust containing Zn and mainly composed of carbon) is passed through the dust storage hopper 17 and a part of the recovered dust is vertically melted and reduced by the dust circulation device 18. It is blown into the furnace from the upper tuyeres 2a of the furnace 1.

A part of the dust collected in the dust collecting hopper 17 is discharged to the transportation device 11 via the dust discharging device 19.

A weight measuring device 20 and dust level meters 21a and 21b are arranged in the dust storage hopper 17 to detect the amount of collected dust and the level position of the dust, and to balance the amount of dust collected by the cyclone 16. Like tuyere 2a
The amount of dust that is circulated in the dust and the amount of dust that is discharged to the dust transport device 11 are adjusted.

600-80 discharged from the vertical smelting reduction furnace 1
Exhaust gas at 0 ° C and fine dust that was not collected by the cyclone 16 are approximately heat-exchanged by the cooling water pipe 7a of the cooling device 7.
After being cooled to 150 ℃ or less, most of the dust sent to the bag filter 9 is collected here, and the cutting device 22,23
After that, it is discharged to the outside of the system as crude ZnO that is cut out and concentrated in the transportation device 11.

[0043]

【Example】

Example 1 Using a vertical smelting reduction furnace having the configuration shown in FIG. 1 and having the following specifications, electric furnace dust was treated (Zn recovery), and the operating condition at that time was investigated.

1) Smelting reduction furnace Diameter: 1.2 m Height: 8.0 m Tuyere: Upper and lower stages 3 each Secondary combustion lance: 2 2) Blower conditions Blower rate: 1650 Nm ³ / hr Blower temperature: 900 ℃ Enriched oxygen amount: 50-200Nm ³ / hr 3) Powder injection Powder mixture ratio: Electric furnace dust: 85% Solvent 15% (solvent type: limestone + silica stone) Injection amount: 600-800kg / hr

The results are shown in Table 1 together with the operating conditions.

[0046]

[Table 1]

In the conformity example in which the furnace top temperature of the smelting reduction furnace was properly adjusted by the secondary combustion of the exhaust gas according to the content of ZnO in the electric furnace dust, in comparison with the comparative example, there were problems such as ventilation fluctuation and hanging. It was confirmed that stable operation was possible. In addition, the Zn concentration of the powder containing ZnO as a main component recovered at this time is as high as 50 to 60%. Regarding metals, the composition is 88 to 92% Fe and 0.7 to 3.5% Cr. ,
It was possible to obtain pig iron containing 3.0-6.0% Mn.

Example 2 A melting test was conducted under the following conditions using an electric furnace dust having the composition shown in Table 2 using a vertical smelting reduction furnace having the configuration shown in FIG. 1 and having the following specifications. . Conditions 1) Smelting reduction furnace Diameter: 1.2 m Height: 8.0 m Tuyere: Upper and lower 3 in each 2) Blower conditions Blower volume: 1650 Nm ³ / hr Blower temperature: 900 ℃ Enriched oxygen amount: 50-200 Nm ³ / hr 3) Powder injection Mixing ratio: Electric furnace dust 90%: Solvent (limestone + silica stone) 10% Injection rate: 600-800kg / hr

[0049]

[Table 2]

The results of this test are shown in Table 3 together with the test conditions.

[0051]

[Table 3]

As shown in Table 3, in the example of the present invention in which the amount of dust discharged to the outside was adjusted while the zinc-containing dust collected by the cyclone was circulated to the upper tuyeres in an appropriate amount, a high concentration of Zn dust was collected as compared with the comparative example. It became possible to do.

The metal composition obtained at that time is 90
~ 93% Fe, 1-2% Si, 4.0-4.3% C, 0.8-1.3%
It was a pig iron containing Mn of 0.6 to 1.0% Cr. In addition, the slag composition is 24-26% SiO ₂ , 15-24% Al ₂ O ₃ , 20-25%.
CaO, 2.3-2.7% MgO, 5.7-7.0% MnO 0.01% or less
It was a slag containing Cd.

[0054]

As described above, according to the present invention, the valuable metal compound containing Zn as a main component can be efficiently recovered from the powdery electric furnace dust without adverse effects such as air flow fluctuation and hanging. . In addition, by recycling the dust generated in the furnace, it is possible to collect high-concentration Zn dust and separate and collect hot metal, which enables effective use of valuable metals and resources, and reduces processing costs compared to conventional processing methods. Can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of equipment suitable for carrying out the present invention.

[Fig. 2] Fig. 1 shows the temperature of the top of the smelting reduction furnace, the degree of oxidation of the top gas ((CO ₂ + H ₂ O) / (CO + CO ₂ + H ₂ O + H ₂ O)), and the presence of Zn in the top gas. It is a figure showing the relation of form (Zn vapor or ZnO).

FIG. 2 is a furnace top of a smelting reduction furnace. When the furnace top gas is burnt, the furnace top temperature and the oxidation degree of the furnace top gas ((CO ₂ + H ₂ O)
Is a diagram showing the relationship of / existence form of _{(CO + CO 2 + H 2} + H 2 O)) Zn changes and furnace top gas of (Zn vapor or ZnO).

FIG. 4 is a diagram showing equipment having a structure for secondarily burning furnace top gas.

FIG. 5 is a diagram showing a configuration of equipment for re-injecting dust generated in the furnace.

[Explanation of symbols]

 1 Vertical smelting reduction furnace 2a Tuyer 2b Tuyer 3 Pipe line 4 Hot air generator 5 Blower 6 Carbon material hopper 7 Exhaust gas cooler 8 Cyclone 9 Bag filter 10a Hopper 10b Hopper 11 Transport device 12a Secondary combustion lance 12b 2 Secondary combustion lance 13 Thermometer 14 Control device 15 Powder blowing device 16 Cyclone 17 Dust holding hopper 18 Dust circulating device 19 Dust discharging device 20 Weighing instrument 21a, 21b Dust level meter 22 Cutting device 23 Cutting device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location C22B 7/02 A B09B 3/00 303 A (72) Inventor Hiroshi Itaya Kawasaki, Chuo-ku, Chiba City, Chiba Prefecture Town No. 1 Kawasaki Iron & Steel Co., Ltd. Steel Research Laboratory (72) Inventor Tetsuya Fujii No. 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Steel Research Laboratory

Claims (3)

[Claims] 1. A zinc-containing dust such as electric furnace dust is blown through a tuyere into a vertical smelting reduction furnace having a carbon-based solid reducing agent-filled layer to reduce and evaporate a zinc content in the dust. When recovering zinc by cooling the exhaust gas containing this evaporated zinc vapor outside the furnace, keep the furnace top temperature of the vertical smelting reduction furnace at 600 ° C or higher while blowing the zinc-containing dust. A method for recovering zinc from zinc-containing dust, comprising: 2. The method according to claim 1, wherein the furnace top temperature of the vertical smelting reduction furnace is adjusted by a plurality of combustion lances for secondary combustion of the exhaust gas generated in the furnace. 3. The method according to claim 1, wherein all or a part of the dust generated in the vertical smelting reduction furnace is blown into the vertical smelting reduction furnace again through the tuyere.