JPH0452234A - Method for separating and recovering metallic component from collected dust - Google Patents

Abstract

PURPOSE:To separate and recover metallic components with high purity at a low cost by mixing collected dust with a binder or carbonaceous powder together with this binder, pelletizing this mixture and subjecting the obtd. pellet independently or the mixture of this pellet with carbonaceous grains to reduction under heating in a reducing atmosphere at a specified temp. CONSTITUTION:A dust pellet 1 contg. carbonaceous powder and/or mixed with carbonaceous grains is charged to a reducing chamber 3. The reducing chamber 3 is closed with only an exhaust port 8 for an exhausting gas left and is cut off from air. The reduction of the pellet 1 is allowed to progress by igniting a gas in a combustion chamber 6 by a burner 5 and heating the inside of the reducing chamber 3 to 1000 to 1400 deg.C. The exhausting gas including zinc, lead, CO, CO2 or the like generated by the reduction is exhausted from the exhaust port 8 and is introduced into a conduit 9. At the time of obtaining zinc components in the shape of powder in which zinc oxide is largely mixed, the exhausting gas is fed to a dust collecting apparatus continuing from a multi- cyclone 11 to a bag filter 12 by a valve 10. On the other hand, the remaining reduced iron in the reducing chamber 3 is recovered.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a method for effectively separating and recovering metallic components contained in dust discharged from an electric furnace for steelmaking. It relates to a method of separation and recovery.

[Conventional technology]

For example, steelmaking operations performed in electric arc furnaces use large amounts of oxygen. Therefore, Zn and P contained in the raw materials
Metals such as b, Fe, etc. are oxidized, and these oxides are generated as fine dust. Considering the current situation where the disposal of industrial waste has become a social issue, it is not possible to simply dump the collected dust, and steel companies are working hard to dispose of it, which costs a large amount of money. It is in a state of being. on the other hand,
In order to effectively utilize the metallic components of this collected dust, attempts have been made for some time to reduce the dust and separate and recover the metallic components. Namely, (A) a method in which collected dust is granulated into pellets and then heated and reduced in a rotary furnace, (B) a method in which dust is injected into hot metal and oxides are reduced by carbon and silicon in pig iron, and (C) a method in which oxides are reduced by carbon and silicon in pig iron. A method of heating reduction using an arc, etc.

[Problem to be solved by the invention]

However, with methods (A) and (B), it is difficult to obtain metallic components with high purity, and with method (C), there are problems in terms of practicality and profitability, such as high electricity costs. .

The present invention has been made in view of these problems, and provides a method for separating and recovering metallic components contained in collected dust as high-purity metallic components at low cost. The purpose is to provide

[Means for Solving the Problems] The method of recovering metallic components from collected dust of the present invention is as follows: a) Adding only a binder or a binder and carbonaceous powder to collected dust and forming it into pellets. granulation step, b) the pellets granulated by this granulation alone, or at least mixed with carbonaceous powder when the pellets do not contain carbonaceous powder, at 1000°C to 1400°C under a reducing atmosphere; a step of thermal reduction; C) a step of recovering zinc alone or in a form containing lead in the form of a melt or powder from the gas escaping from the pellets or pellets and carbonaceous grains by this thermal reduction; and d ) The gist is that the process includes a step of recovering iron remaining through thermal reduction.

The steps included in the present invention are as follows.

a) Pre-treatment of collected dust For example, collected dust generated in an electric furnace is extremely fine and difficult to transport and reduce as it is. Therefore, first, a binder is added to the collected dust, and pellets having the required strength are produced using a baitizer such as a dish-type granulator. As a binder, pulp waste liquid,
Molasses etc. are used industrially.

At this time, in order to reduce the metal oxides contained in the dust, carbonaceous powder as fine as possible, preferably having a particle size of 3 square centimeters or less, can be mixed with the collected dust to form pellets.

The carbonaceous powder that can be used may be one with a high carbon content (for example, coke powder, coal powder, etc.). If the temperature is too high, it becomes difficult to escape CO, CO2, and vaporized gases such as zinc and lead generated during reduction.

Therefore, it is desirable that the average particle size is 5 to 30 mm.

The produced pellets can be sent as is to the next process, but in order to shorten the time of the next process and stabilize the work, they are sometimes dried at low temperatures to improve the strength of the pellets. The low temperature here refers to a temperature at which reduction of dust does not begin, and is preferably about 300"C or less.

b) Heat reduction of pellets The dust pellets obtained in step a) are heat reduced either alone or after being mixed with carbonaceous particles. The carbonaceous particles may have a high carbon content, and may be, for example, commercially available carbon particles. These carbonaceous particles, like the carbonaceous powder described above, are used to reduce metal oxides contained in the dust pellets. Therefore, the carbonaceous powder described above,
Although this carbonaceous powder can be used in combination with the carbonaceous powder, it is also possible to use only the carbonaceous powder alone, which has good reactivity with dust, or to use only the carbonaceous powder alone for convenience if carbonaceous powder is available at a low price. It is also possible to use The amount of these carbonaceous powders and carbonaceous grains to be used can be determined in consideration of conditions such as their carbon content, dust components and composition, and reactivity with dust. Normally, when each is used alone, the carbon content of carbonaceous powder or carbonaceous particles is at most 30% of the weight of the dust, and when used together, the carbon content of each may be less than 30%, and It is sufficient if the total amount of carbon added is about 30%.

If the amount of these carbonaceous powders and/or carbonaceous particles is small, the metal oxide will not be reduced sufficiently, and if the amount is too much than the equivalent amount to reduce the metal oxide, the cost of fuel and materials will only increase. However, because of the conditions described above, it is not limited to this numerical value.

Further, the particle size of the carbonaceous particles is preferably 5 to 30 fflIn on average, similar to the above-mentioned dust pellets.

Reduction is carried out by cutting off air and heating from the outside in a so-called steamed state. The temperature at this time is 1000℃~1
The temperature is selected to be within the range of 400°C.

The reason why the temperature was set at 1000"C or higher is that among iron oxide, zinc oxide, and lead oxide, zinc oxide starts to be reduced at the highest temperature, and its starting temperature is around 1060°C. Also, 1400"C The reason for the following is that if the temperature exceeds 1400''C, the reduced iron will be sucked back and melted, making recovery difficult.The heating time is preferably 3 hours or more, although it depends on the heating temperature.

Since the metallic zinc produced by the reduction has a boiling point of about 900° C., it becomes a gas and escapes from the pellets, or from the pellets and carbonaceous grains together with C0JpC0. At this time, if the CO□ concentration is high or if it is exposed to air at a high temperature, the zinc will oxidize and become zinc oxide again. Depending on the application, it is possible to recover and use zinc oxide, but if you want to obtain metallic zinc with high purity, a reducing gas such as CO or an inert gas such as Nt should be introduced into the exhaust gas. It is effective to prevent oxidation.

C) Recovery of zinc or zinc and lead When oxidation of zinc is prevented as described above, zinc is obtained in the form of metallic zinc. Since the melting point of zinc is about 420℃ and the boiling point is about 900℃, the temperature of the escaping gas is about 400℃~
When the temperature is between 900°C, zinc is melted and obtained in a molten state. Recovered zinc often contains a portion of lead as a solid solution. However, since lead is usually in a very small amount, it is recovered in the form contained in zinc unless it is particularly needed, but if it becomes a problem from a usage or market price point of view, it can be recovered using the well-known phase diagram. They may be separated according to their solubility.

On the other hand, when the above-mentioned reducing gas or inert gas is not introduced to prevent zinc oxidation, the CO in the escape gas
2 When the concentration is high or when it comes into contact with air, some of the zinc oxidizes and becomes zinc oxide again. The melting point of zinc oxide is approximately 19
Since the temperature is as high as 80° C., this zinc oxide is discharged in powder form along with the fugitive gas and the remaining zinc metal. This powdered zinc oxide can be collected and collected using a multi-cyclone, bag filter, etc. At this time, a portion of lead is also oxidized to become powdered lead oxide, which coexists in zinc oxide.

Since this lead oxide is also in a trace amount, it is unlikely to be a problem, although it depends on the application. As mentioned above, depending on the use and market price, zinc can be recovered and used in the form of a mixture of metallic zinc and zinc oxide in powder form, or mostly in the form of zinc oxide. You can also.

The exhaust gas after recovering zinc or zinc and lead contains a large amount of carbon monoxide, so it can be used as fuel.

d) Recovery of iron When the dust pellet is reduced, zinc, lead, oxygen, etc. are released from the pellet, and later a porous part consisting of raw reduced iron and some iron are melted together with carbon. A melted part remains. These porous portions containing reduced iron and the molten portion can be recovered and used as raw materials for electric furnaces while still hot or after cooling.

[For production]

The greatest feature of the present invention is that metal oxides contained in pellets obtained by processing collected dust are converted into carbonaceous powder and/or
Alternatively, it is reduced by carbon in carbonaceous particles to produce a simple metal. The main reactions during this reduction are as follows.

2 ZnO+ C→2 Zn + C0z2FeO+
C-)2Fe + C0z2PbO+ C→2Pb
+ Co□CO□ +C→2CO Z n O+ CO→Z n 10CotF e O+
CO-F e + CChPbO+ Co →Pb
+ CO2 However, since Fezes, Fe30a, PbzO, PbzO4, etc. can coexist as oxides of iron and lead, the reaction that actually occurs is thought to be more complicated.

Among the produced metallic zinc, metallic lead, and metallic iron, zinc has the lowest boiling point (approximately 900°C) and has a reduction temperature of 1000°C to 1
By being held at 400°C, it vaporizes and escapes. Iron has a much higher boiling point (approximately 2700°C), so it does not vaporize and remains. While performing the reduction in this manner, the zinc and iron components of the metallic components contained in the dust are separated due to the difference in volatility at the reduction temperature.

Lead has a boiling point intermediate between these two metals (approximately 1
700''C), both phenomena may occur, such as vaporization together with zinc or remaining together with iron.In either case, the amount is so small that it rarely causes a problem.

Zinc once becomes a single metal together with some lead and evaporates, but because it is easily oxidized, C in the escaping gas
A part of it becomes zinc oxide again due to O2 and O2 in the air. The melting point of zinc oxide is higher than the temperature of the escaping gas (approximately 19
80°C) and recovered in powder form. C in the escaping gas
By introducing a reducing gas such as O or an inert gas such as N2, oxidation of zinc is suppressed and the zinc is mainly recovered as a molten metal. Lead vaporized together with zinc,
These powders or melts are recovered together with zinc.

Iron remains as a porous metallic solid since its melting point is also above the reduction temperature (approximately 1500° C.). However, some iron may have a lower melting point due to the solid solution of carbon, and may remain in a molten state.

In this way, it becomes possible to separate and recover the zinc content, or the zinc content, the lead content, and the iron content from among the several types of metal oxides contained in the collected dust.

〔Example〕

Next, a specific embodiment of the present invention will be described.

FIGS. 1 and 2 are diagrams showing an example of an apparatus in which a coke oven is applied to the method of the present invention.

Dust pellets l containing carbonaceous powder and/or mixed with carbonaceous powder are charged from a raw material storage hopper 2 into a reduction chamber 3 made of refractory material. Reduction chamber 3 is Beret 1
In order to sequentially charge and reduce the
Since each of the 40 reduction chambers 3 arranged in a row is long and narrow,
Usually, it has two opening/closing raw material charging ports 4, one at each end. When charging the dust pellets 1, the charging port 4 is opened, the hopper 2 is attached, and the charging port 4 is closed after the pellets are filled. As a result, the reduction chamber 3 is sealed leaving only the discharge port 8 for the advancing gas, and is isolated from the air. The reduction of the pellet 1 proceeds by igniting and burning the gas in the combustion chamber 6 by the burner 5, and heating the inside of the reduction chamber 3 to a predetermined temperature. A heat storage chamber 7 is provided below the reduction chamber 3, and heat exchange with the reduction chamber 3 is performed.

Escaped gas containing zinc, lead, CO, CO□, etc. generated by the reduction is discharged from the outlet 8 and guided to the exhaust gas conduit 9. The conduit 9 is provided with a switching valve 10, and when the zinc content is to be obtained in the form of a powder containing a large amount of zinc oxide, the valve 10 directs the escape gas from the multicyclone 11 to the bag filter 12. It is sent to the subsequent dust collector. During this time, at least a portion of the zinc is vaporized, re-oxidized and powdered, and allowed to cool in the atmosphere. The collected powder is collected from the collection port 13. This powder mainly consists of zinc oxide and metallic zinc, and contains trace amounts of lead oxide and the like. On the other hand, when the zinc component is mainly obtained in the form of molten metal zinc, the escape gas is guided to a heat-retaining conduit 14 made of a heat insulating material or the like by the switching valve 1o, and then sent to the metal zinc melting furnace 15. At this time, CO is introduced into the heat retaining conduit 14 from the CO inlet 16 to slowly cool it and prevent the oxidation of zinc, and if zinc oxide has already been produced, it is reduced. The melting furnace 15 is heated to a predetermined temperature by the heater 19, and the zinc remains molten in the melting furnace 15 as a melt together with small amounts of zinc oxide, lead, and the like.

The exhaust gas after the zinc content or zinc content and lead content have been separated is discharged from the bag filter 12 and the melting furnace 15 through the exhaust port 17 and the exhaust gas, respectively, and is used as fuel or the like as the case may be.

After the reduction is completed, the doors 19 and 20 at the front and rear of the reduction chamber 3 are opened, and the remaining reduced iron is pushed out of the reduction chamber 3 by an extruder and collected in a saucer.

Electric furnace dust was reduced using such a device. Table 1 shows the particle size distribution of the dust used. Pellets were prepared by mixing carbonaceous powder with this dust. The particle size distribution and components of this pellet are shown in Tables 2 and 3, respectively.

Fill a 14t 500kg reduction chamber with only these pellets, and use L, N, and G as fuel at 1100°C to 1200°C.
Reduction was carried out by heating at a temperature of 8 hours. Powder containing mainly zinc and zinc oxide was recovered from the fugitive gas by multi-cyclone and bag filter. The components and recovery rate of this powder are shown in Table 4. Furthermore, Table 5 shows the components of the exhaust gas after powder recovery. On the other hand, reduced iron consisting of a porous portion and a molten portion remained in the reduction chamber. This residual reduced iron was recovered and the components were analyzed. The results are shown in Table 6.

In another example, the zinc content was recovered as molten zinc by introducing CO. Table 7 shows the analysis results of the components of the melt recovered together with the molten zinc.

〔Effect of the invention〕

According to the method of the present invention, metallic components can be separated and recovered from collected dust at a much lower cost than conventional methods. Moreover, the recovery rate is extremely good as shown in the examples for the zinc content.

The reason for this is that by forming the collected dust into pellets together with carbonaceous powder and/or mixing the pellets with carbonaceous particles, the metal oxides in the dust can be efficiently reduced by carbon. Moreover, since no special materials or equipment are required, the method can be said to be low in cost and highly practical. As a result of being able to obtain metallic components at low cost and with a high recovery rate, it can be said that a way has been opened for recovering and effectively utilizing metallic components in a sufficiently profitable manner from collected dust, which used to be nothing more than waste.

[Brief explanation of the drawing]

1 and 2 are diagrams showing an example of an apparatus for concretely carrying out the method of the present invention, in which FIG. 1 is a front sectional view, and FIG. FIG. 1...Dust pellets 3...Reduction chamber 5...Burner 6...Combustion chamber 9...Escape gas conduit 10...Switching valve 11...Multi cyclone 12...Bag filter 13...Powder collection port 15...Melting furnace 16...
・CO inlet

Claims (1)

[Claims] 1a) A step of adding only a binder or a binder and carbonaceous powder to the collected dust and granulating it into pellets; b) A step of granulating the pellets by this granulation alone. or at least a step of mixing the pellets with carbonaceous grains when the pellets do not contain carbonaceous powder and heating and reducing the mixture at 1,000°C to 1,400°C in a reducing atmosphere; c) This heating reduction causes the pellets to escape from the pellets, or from the pellets and the carbonaceous grains. A process of recovering zinc alone or containing lead in the form of melt or powder from the emitted gas, and d) recovering residual iron by thermal reduction.Metallic components from collected dust. How to separate and recover. 2. The method according to claim 1, wherein the carbonaceous powder has a particle size of 3 mm or less. 3. The method according to claim 1, wherein the average particle size of each of the pellets and carbonaceous particles is 5 to 30 mm.