JP3336131B2 - Method for recovering zinc from zinc-containing dust - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention aims 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.

[0003] For example, self-generated scrap (iron scrap generated in the steel making process) has a clear identity and contains little impurities, so that most of it is consumed in a generating plant. On the other hand, secondary processing scrap and waste scrap are separated and collected after secondary processing of steel products and integrated into final products, so they contain a lot of scraps of surface-treated steel sheets and special steel. Are refined and reused in electric furnace manufacturers.

[0004] The electric furnace dust generated at that time contains elements such as chromium, cadmium, and lead which are eluted when disposed of in a landfill and cause environmental pollution, depending on the impurity of the raw material, by several percent. Is 20-40% and iron is 25-50
%, And it is strongly desired to treat and recycle them, that is, to inexpensively fix harmful metals such as chromium, cadmium and lead, and to recover and recycle valuable metals such as Zn and Fe. .

[0005] As a prior art relating to this point, for example, Japanese Patent Application Laid-Open No. 64-980081 discloses that electric furnace dust is agglomerated, and the agglomerated electric furnace dust is added to a molten steelmaking slag together with a reducing agent. A method has been proposed in which valuable metal compounds mainly composed of Zn melted and volatilized by oxygen gas bubbling are recovered and harmful elements are fixed in slag. Japanese Patent Application Laid-Open No. 2-38535 discloses that electric furnace dust is
Supplied together with a reducing agent and a flux to a gas-tight electric furnace,
A method of recovering volatile metals in the form of dust and recovering valuable metals such as Fe in the form of molten metal is disclosed in
Japanese Unexamined Patent Publication No. 5-65552 discloses a flash reactor type melting processing furnace using a burner composed of oxygen-based combustion gas and fuel injection as a novel electric furnace dust treatment method.

[0006]

The problem to be solved by the invention
In the method disclosed in Japanese Patent Publication No. 0081, a step of agglomerating electric furnace dust needs to be separately added, and there is a problem in that it is difficult to recover and recycle valuable metals such as Fe.

In the method disclosed in Japanese Patent Application Laid-Open No. 2-38535, steel having a low valuable metal content is produced using an electric furnace. Require the use of a large amount of oxygen, so that both methods are expensive treatment and recovery methods.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate volatile aggressive metals contained in dust such as electric furnace dust, especially zinc, without causing an increase in cost (to avoid agglomeration of dust). Use as little electrical 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.) The idea is to propose a new method that can be recovered.

[0009]

According to the present invention, there is provided a vertical smelting reduction furnace provided with a packed bed of a carbon-based solid reducing agent, and having two upper and lower tuyeres connected to a hot air generator via a pipeline. Injecting zinc-containing dust such as electric furnace dust, reducing and evaporating the zinc content in the dust, and recovering zinc by cooling the exhaust gas containing the evaporated zinc vapor outside the furnace, The zinc-containing dust was blown together with hot air through the upper tuyere, and hot air was blown from the lower tuyere, and while blowing the zinc-containing dust, the furnace top temperature of the vertical reduction furnace was generated in the furnace. A method for recovering zinc from zinc-containing dust, characterized in that the exhaust gas is maintained at a temperature of 600 ° C. or higher by a plurality of combustion lances for secondary combustion.

In the above method, it is preferable that all or a part of dust generated in the vertical smelting reduction furnace is blown into the vertical smelting reduction furnace again through the upper tuyere.

[0011]

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

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

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

Reference numeral 8 denotes a cyclone connected to the gas cooling device 7, reference numeral 9 denotes a bag filter arranged behind the cyclone 8, reference numerals 10a and 10b denote the cyclone 8, the bag filter 9
A hopper for feeding the dust (metal zinc or zinc oxide) collected by the hopper to the transport device 11, and 12a and 12b are lances for secondary combustion arranged at the upper part of the smelting reduction furnace 1. The lances 12a and 12b blow the oxygen or air by opening and closing the valves V ₁ and V ₂ (flow rate regulators) in accordance with the measurement result of the thermometer 13 according to a command from the control device 14, and the furnace of the vertical smelting reduction furnace 1 Adjust so that the temperature at the top is the proper temperature. Reference numeral 15 denotes a powder blowing device for cutting out an appropriate amount of zinc-containing dust (electric furnace dust or the like) and blowing it into the smelting reduction furnace 1, which is added for the purpose of adjusting the viscosity of slag and the liquidus temperature. A smelting solvent is mixed in a predetermined ratio.

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

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

The zinc-containing dust (electric furnace dust, etc.) is mixed in a predetermined ratio with a smelting solvent for limestone and silica stone added in advance for the purpose of adjusting the viscosity of slag and the liquidus temperature. 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, and is discharged from the furnace top duct through the carbon material packed bed c.

The iron oxide in the zinc-containing dust is chromium,
Together with other oxides such as cadmium, the carbon material is melted in the tuyere-tip raceway by the heat of combustion of the carbonaceous material and descends toward the lower tuyere 2b. And this descending molten material is tuyere 2b
At the same time as the high-temperature reducing gas generated at the end of the reactor, it is reduced by direct contact with the packed layer c during the dropping, and is separated into metal and slag. At this time, the heat of the reduction reaction, 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 hole 1a, and the slag is discharged from the slag port 1b. Chromium, cadmium and the like are also fixed in the molten metal or slag. And be rendered harmless.

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

In the treatment of electric furnace dust using a carbon-packed bed-type smelting reduction furnace, since electric furnace dust contains a large amount of oxides of volatile elements such as zinc oxide, airflow inhibition and Operation troubles such as hanging of shelves frequently occur, and operation in the smelting reduction furnace becomes unstable.

As a result of repeated examinations and experiments in order to investigate such causes, the following has been clarified.

(1) When obstruction of ventilation or hanging on the shelf occurs, a large amount of deposits mainly composed of a mixture of ZnO and C are observed on the surface of the carbon material at the top of the furnace and on the wall surface of the furnace top. (2) Inhibition of ventilation and hanging on the shelves 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 carbon material which is estimated to have high reducibility. (4) When the top temperature is low, the top temperature and the oxidation degree of the top gas ((CO ₂ + H ₂ O) / (CO + CO ₂ + H ₂ + H ₂ O)), the presence of Zn in the top gas The form (Zn vapor or ZnO) was in the situation as shown in FIG. (5) The Zn vapor pressure of the top gas changes according to the zinc content of the electric furnace dust, but within the operating range possible with the method of the present invention, measurement by a top mass spectrometer or rapid aggregation of the collected gas From the chemical analysis values of the collected aggregates and the values calculated and estimated from the amount of collected gas, it was clear that the values were about 0.01 to 0.1 atm. (6) From the above, in the operation of a vertical smelting reduction furnace (one with two-stage tuyere), the presence form of Zn in the furnace top gas was changed to Zn vapor, and the operation troubles such as airflow inhibition and shelf hanging were reduced. To ensure stable operation of the smelting reduction furnace without causing it to occur, the furnace top temperature must be 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 the furnace top temperature is to be maintained at 600 ° C. or higher, it must be lower than 600 ° C. There is. Therefore, in the present invention, the exhaust gas is burned using the secondary combustion lances 12a and 12b provided on the furnace top.

If the exhaust gas is burned using such secondary combustion lances 12a and 12b, the presence form of Zn in the furnace top gas becomes Zn vapor, and operation troubles such as obstruction of ventilation and hanging on a shelf are reduced. A stable operation can be performed without raising.

The furnace top temperature which must be achieved by the secondary combustion is desirably in accordance with the condition shown in FIG. 3, which is determined by the furnace top temperature before the secondary combustion and the partial pressure of Zn vapor in the furnace gas. .

For example, the furnace top temperature before the secondary combustion is 500 ° C.
When the oxidation degree of the top gas is 0.8 and the partial pressure of Zn vapor in the top gas at that time is 0.1 atm, the oxidation degree increases due to the secondary combustion, as is clear from FIG. Considering the effect of increasing the temperature of the furnace and the effect of increasing the furnace top temperature, the furnace top temperature after the secondary combustion becomes 1000 ° C. or more.

It is not advisable to simply raise the temperature at the top of the furnace, as this will cause damage to the refractory. Therefore, it is preferable to adjust the temperature so as to have an appropriate furnace top temperature as shown in FIG. 3 taking into consideration the partial pressure of Zn vapor measured by a mass spectrometer or the like together with the temperature measurement result at the furnace top. . Regarding the furnace top temperature, 1200 ° C or less can be said to be an appropriate temperature.

In the equipment having the configuration as shown in FIG. 1 described 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. Since Zn vapor or Zn oxide is fine particles with a particle size of 3 μm or less, which are quasi-particles and become very fine particles of 5 to 10 μm, it is not possible to use a fine dust collector such as a back filter as it is. This is because it becomes difficult. FIG. 4 shows an example of the configuration of the equipment having no secondary combustion lance.

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

In the present invention, as described above, zinc oxide contained in the electric furnace dust blown from the upper tuyere 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.

(1) In addition to Zn, a large amount of carbon and ash of coke, which is a carbon-based solid reducing agent, is mixed into the exhaust gas from the vertical smelting reduction furnace in a large amount. A decline is inevitable. (2) Since some Fe is contained in the dust flying out of the vertical smelting reduction furnace, a reduction in the amount of recovered metal, that is, a decrease in productivity is inevitable. (3) If the amount of fine powder carbon that jumps out of the vertical smelting reduction furnace increases, the carbonaceous unit consumption increases, and an increase in production cost is inevitable.

According to the present invention, the whole or a part of the dust generated in the molten vertical reduction furnace is blown into the furnace again through the tuyere to convert the volatile valuable metal mainly composed of Zn into the purest possible form. This is extremely advantageous not only for recycling but also for reusing the carbonaceous material in the dust and recovering the low-boiling-point valuable metals such as Fe in the dust at a high yield.

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

In order to further increase the Zn concentration and to effectively utilize the carbon in the collected dust, a dust collector such as a cyclone 16 is disposed downstream of the vertical smelting reduction furnace 1 and a cooling device 7 as shown in FIG. It is effective to place it in the previous stage.

First, when the cooling device 7 is disposed directly on the outlet side of the vertical smelting reduction furnace 1 without installing the cyclone 16, Zn vapor discharged from the top of the reduction furnace 1 is again cooled by the cooling device 7.
Although collected as ZnO, the dust thus obtained (hereinafter referred to as “recovered dust”) contains a large amount of carbon derived from the 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 of the Zn content and the carbon and ash content jumping out of the vertical smelting reduction furnace 1 is removed. Among them, dust containing relatively coarse carbon content of about 10 μm or more generated from carbonaceous materials can be collected by the cyclone 16 and most of the carbon content contained in the dust can be separated. hand
The Zn content is to be recovered. Therefore, (1) By separating the carbon content, the Zn concentration in the recovered material in a cooling device or a bag filter can be improved. (2) Since the carbon content recovered by the cyclone can be recycled, it is effective to reduce the carbon unit consumption of the vertical smelting reduction furnace. (3) Metals such as Fe contained in the dust collected by the cyclone can be recycled, so that a reduction in metal productivity can be avoided.

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 at the subsequent stage, a large amount of carbon caused by the carbon material accumulates in the cooling device 7. Therefore, it is appropriate to dispose the dust collecting device such as the cyclone 16 at a stage after the vertical smelting reduction furnace 1 and before the cooling device 7.

The dust collected by the cyclone 16 (dust containing Zn and mainly composed of carbon) passes through a dust storage hopper 17 and a part of the collected dust is vertically melt-reduced by a dust circulator 18. It is blown into the furnace from the upper tuyere 2a of the furnace 1.

A part of the collected dust in the dust collecting hopper 17 is discharged to the transport 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. Tuyere 2a
The amount of dust to be circulated to and the amount of dust discharged to the dust transport device 11 are adjusted.

600 to 80 discharged from the vertical smelting reduction furnace 1
The exhaust gas at 0 ° C and the fine dust not collected by the cyclone 16 are subjected to heat exchange by the cooling water pipe 7a of the
After being cooled to 150 ° C. or less, most of the dust sent to the bag filter 9 is collected here and cut out by the cutting devices 22 and 23.
Through the transport device 11 and discharged out of the system as concentrated ZnO.

[0043]

【Example】

Example 1 An electric furnace dust was treated (recovery of Zn) using a vertical smelting reduction furnace having the following specifications and having the configuration shown in FIG. 1, and the operation status at that time was investigated.

1) Smelting reduction furnace Furnace diameter: 1.2 m Height: 8.0 m Tuyere: upper and lower three each Secondary combustion lance: two 2) Ventilation conditions Ventilation volume: 1650 Nm ³ / hr Ventilation temperature: 900 ° C. enriched oxygen content: 50 to 200 nm ³ / hr 3) powder blown powder blending ratio: electric arc furnace dust: 85% solvent 15% (solvent type: limestone + Keiseki) blown amount: 600 ~800kg / hr

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

[0046]

[Table 1]

In the adaptation example in which the furnace top temperature of the smelting reduction furnace was appropriately adjusted by the secondary combustion of the exhaust gas in accordance with the content of ZnO in the electric furnace dust, troubles such as variation in ventilation and hanging on the shelf were found as compared with the comparative example. It was confirmed that stable operation was possible. The Zn concentration of the ZnO 2 powder recovered at this time is as high as 50 to 60%, and as for the metal, the composition is 88 to 92% of Fe and 0.7 to 3.5% of Cr. ,
Pig iron containing 3.0 to 6.0% Mn could be obtained.

Example 2 Using a vertical smelting reduction furnace having the following specifications and having a configuration as shown in FIG. 1, a melting test was carried out under the following conditions using electric furnace dust having the composition shown in Table 2. . Condition 1) smelting reduction furnace Ro径: 1.2 m Height: 8.0 m tuyeres: upper, lower each triplet 2) blowing condition air volume: 1650 nm ³ / hr blast temperature: 900 ° C.-enriched oxygen content: 50 to 200 nm ³ / hr 3) Powder injection Mixing ratio: Electric furnace dust 90%: Solvent (limestone + silica stone) 10% Injection amount: 600 to 800kg / hr

[0049]

[Table 2]

Table 3 shows the results of this test together with the test conditions.

[0051]

[Table 3]

As shown in Table 3, the zinc-containing dust collected by the cyclone was circulated to the upper tuyere in an appropriate amount, and the amount of dust discharged to the outside was adjusted in the present invention example. In comparison with the comparative example, a higher concentration of Zn dust was recovered. 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%
Of pig iron containing 0.6% to 1.0% Cr. Moreover, the slag composition SiO ₂ 24-26% 15-24% of 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, valuable metal compounds mainly composed of Zn can be efficiently recovered from powdery electric furnace dust without adverse effects such as fluctuations in ventilation and hanging on shelves. . In addition, by recycling the dust generated in the furnace, high-concentration Zn dust can be recovered and hot metal can be separated and recovered, making it possible to use valuable metals and resources more effectively and reducing processing costs compared to conventional processing methods. Reduction can be achieved.

[Brief description of the drawings]

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

FIG. 1 shows the top temperature of the smelting reduction furnace and the oxidation degree 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 FIG. 3 is a diagram showing a relationship between forms (Zn vapor or ZnO).

FIG. 2 is a top view of a smelting reduction furnace, in which a top gas and a degree of oxidation of a top gas ((CO ₂ + H ₂ O)
FIG. 4 is a diagram showing a relationship between a change in / (CO + CO ₂ + H ₂ + H ₂ O)) and a form of Zn present in the furnace top gas (Zn vapor or ZnO).

FIG. 4 is a diagram showing equipment having a structure for performing secondary combustion of furnace top gas.

FIG. 5 is a diagram showing a configuration of a facility for re-blowing dust generated in a furnace.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vertical smelting reduction furnace 2a Tuyere 2b Tuyere 3 Pipe line 4 Hot air generator 5 Blower 6 Carbon material hopper 7 Exhaust gas cooling device 8 Cyclone 9 Bag filter 10a Hopper 10b Hopper 11 Transport device 12a Lance for secondary combustion 12b 2 Lance for the next combustion 13 Thermometer 14 Control device 15 Powder injection device 16 Cyclone 17 Dust retaining hopper 18 Dust circulation device 19 Dust discharge device 20 Weight measuring device 21a, 21b Dust level meter 22 Cutting device 23 Cutting device

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Fujii 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Works, Ltd. Steel Research Laboratory (56) References JP-A-57-13129 (JP, A) JP-A Sho 58-224129 (JP, A) JP-A-62-192513 (JP, A) JP-A-62-182214 (JP, A) JP-A-5-271735 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22B 1/00-61/00

Claims (2)

(57) [Claims] 1. A pipeline comprising a packed layer of a carbon-based solid reducing agent.
A zinc-containing dust such as an electric furnace dust is blown into a vertical smelting reduction furnace having two upper and lower tuyeres connected to a hot-air generator via a hot air generator to reduce and evaporate the zinc content in the dust. In recovering zinc by cooling the exhaust gas containing the evaporated zinc vapor outside the furnace, the zinc-containing dust is blown together with hot air through the upper tuyere , and hot air is blown from the lower tuyere. While blowing the dust, the top temperature of the vertical reduction furnace is
Multiple combustion runs for secondary combustion of exhaust gas generated in
A method for recovering zinc from zinc-containing dust, wherein the temperature is maintained at 600 ° C. or higher by a heat source. 2. The method according to claim 1, wherein all or part of the dust generated in the vertical smelting reduction furnace is blown into the vertical smelting reduction furnace again through the upper tuyere.