JPH0835018A - Method of recovering metal from fly ash - Google Patents

Abstract

(57) [Abstract] [Purpose] Efficiently separates and recovers heavy metals and chlorine contained in CaCl ₂ -containing fly ash generated when shredder dust from abandoned automobiles, home electric appliances, etc. is incinerated and reduced in volume. [Composition] Chlorine generated by burning waste is CaCl
_A method for recovering metal from fly ash, which is fixed and contained as ₂ , comprising: a) heating the fly ash in an oxidizing atmosphere while applying a shearing force to remove chlorine and hydrogen chloride generated by the decomposition of CaCl ₂ ; Reacting with a metal component contained in the ash, b) metal chloride generated and volatilized thereby is dissolved and recovered by contacting with an absorbing solution, and c) the dissolved metal is fractionally separated from the obtained absorbing solution. to recover.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering metals from incinerated fly ash as a technique for recycling waste. To be more specific, shredder dust after crushing scrapped automobiles, scrapped home electric appliances, etc. with a shredder to recover metal,
The present invention relates to a method for recovering metals from fly ash generated when the volume is incinerated or for effectively utilizing the fly ash.

[0002]

2. Description of the Related Art Increasing amounts of various kinds of wastes and their disposal methods have become social problems as a harmful effect on the development of the consumption economy in recent years. At present, body shells after dismantling and collecting valuable parts from abandoned automobiles and large household appliances such as electric washing machines and electric refrigerators are crushed by shredders, and iron and non-ferrous metals are collected. The part called plastic shredder dust, which mainly consists of plastics, is landfilled.

However, the amount of industrial waste and household waste is increasing, and it is becoming more and more difficult to secure the landfill site due to the problems of saturation of existing landfill sites and environmental pollution. Therefore, recycling of waste and reduction of volume are required. Incineration power generation is being studied as a method for recycling and reducing the volume of the shredder dust. That is, it aims to recover and utilize the thermal energy generated by the combustion of plastics, which occupy the main part of shredder dust, by heat exchange in a power generation boiler or the like, and also to reduce the volume as incinerated ash.
The incineration ash generated when the shredder dust is incinerated includes furnace bottom ash (bottom ash) and fly ash (fly ash) contained in the combustion waste gas and collected by a capturing means such as a filter.

In the case of general fly ash such as coal ash, aggregate,
It is reused and disposed of by methods such as conversion to cement raw material, landfill disposal, and stabilization treatment (pelletization).
In fly ash obtained by incinerating shredder dust as described above, chlorine compounds (CaCl2) formed by immobilizing chlorine generated during combustion due to plastic such as polyvinyl chloride with quicklime, limestone, etc., And Cu, Z
Since it contains metals such as n and Pb, it cannot be used as an aggregate or cement raw material due to problems such as strength reduction, corrosion of building materials and environmental friendliness. Even if it is landfilled, it will be landfilled due to acid rain. There is a risk of salt damage due to the elution of chlorine from the disposal site, and there is a risk of environmental pollution due to the elution of heavy metals.
Furthermore, from the viewpoint of resource reuse, it is desired to recover metal components from fly ash.

By the way, conventionally, a chloride roasting method has been known as a method for collecting and separating metals from iron sulfide and copper oxide ores, for example. However, there are known examples of applying this kind of method to fly ash treatment. Has not been done.

[0006]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for efficiently and easily separating and recovering various metals from fly ash generated when incinerating waste such as shredder dust. To do. Another object of the present invention is to provide a method capable of separating and recovering Cl as well.

[0007]

SUMMARY OF THE INVENTION The present inventors have
As a result of intensive research to separate and recover metals in fly ash and to separate and remove chlorine components, it was noted that fly ash obtained by incinerating waste contains CaCl _2. However, if this fly ash is roasted as it is without adding chlorine gas, chlorine and hydrogen chloride are generated by the decomposition of CaCl ₂ , which causes the metal components in the fly ash to be volatilized and separated as chlorides. I got the knowledge of. Furthermore, as a result of studies to enhance the recovery efficiency, it was found that the recovery efficiency was improved by performing attrition, agitation and the like during roasting with chloride. In the case of chlorination roasting of general ores, chlorine, NaCl, etc. must be newly added during roasting,
It was concluded that attrition and fumarolic stirring are not necessary, but in the case of fly ash, such attrition and fumarolic stirring are essential for improving the yield. This is because the form of metal components in fly ash is different from that in general ores. The present inventors have arrived at the present invention based on such new knowledge.

That is, the present invention relates to a method for recovering metal from fly ash containing chlorine, which is generated by burning waste and fixed as CaCl ₂ , and comprising: a) rubbing the fly ash in an oxidizing atmosphere. By heating while applying shearing force, the chlorine and hydrogen chloride generated by the decomposition of CaCl2 are reacted with the metal components contained in the fly ash, and b) the metal chloride thus generated and volatilized is brought into contact with the absorbing liquid. Dissolving and recovering by dissolving, and c) a method for recovering metal from fly ash, characterized in that dissolved metal is separated and recovered from the obtained recovery liquid.

In the step c), i) sulfuric acid is added to the recovery liquid to precipitate lead as PbSO ₄ to recover it, and then the pH is adjusted to 2 to 4 and then Cu is precipitated by contacting with iron pieces. Then, ii) Ca (OH) ₂ or CaCO ₃ is added to the residual liquid to precipitate Fe (OH) ₃ , which is then filtered to recover Fe, and iii) Na ₂ is added to the filtered liquid after filtration. CO ₃ is added to neutralize,
ZnCO ₃ is precipitated, filtered to recover Zn, and iv) a step of evaporating and concentrating the filtered solution after filtration to recover NaCl, whereby not only metal components in fly ash but also The chlorine component can also be recovered.

[0010]

The present invention will be described in detail below by taking as an example a series of treatment processes of shredder dust from abandoned automobiles and abandoned home electric appliances, which incorporates the metal recovery method from incinerated fly ash according to the present invention.

After collecting reusable parts, scrap automobiles and waste home electric appliances are crushed by a shredder in accordance with a conventional method to recover ferrous and non-ferrous metals. The shredder dust, which is mainly made of plastic after recovery, is burned to reduce the volume, but 1000 ° C or lower in order to prevent generation of harmful components such as dioxins due to burning.
More preferably, for example, a fluidized roasting furnace or a grate furnace is used so that it can be incinerated at a temperature of 700 to 900 ° C. The heat energy generated at this time is heat-exchanged and recovered in the power generation boiler. In addition, during this combustion, a large amount of chlorine is generated due to plastic such as polyvinyl chloride, but shredder dust 100 is generated during incineration.
By adding 5 to 30 parts by weight of slaked lime or limestone to parts by weight and fixing chlorine as calcium chloride (CaCl ₂ ), harmful chlorine gas is prevented from being released. Then, the bottom ash, which has been reduced in volume after incineration and remains in the furnace, is subjected to a recovery process of contained metal.

On the other hand, the fly ash contained in the combustion flue gas is captured and collected by a dust collector, which is provided in the middle of the flue and is composed of a filter or the like. The average particle size of this fly ash is about 0.1 to 10 μm, and particles of 1 to 8 μm account for 30 to 70% of the whole. And, as described above, a large amount of CaCl ₂ and metals are present in this fly ash.

In the present invention, the fly ash is first recovered as it is or when the chlorine content is insufficient, the recovered NaCl is recovered.
After adding an appropriate amount, while circulating air, for example, 60
It is heated and roasted at a temperature of 0 to 1000 ° C, preferably 650 to 750 ° C. At the time of roasting such fly ash, in order to improve the metal recovery efficiency, for example, attrition,
It is desirable to apply a shearing force to the fly ash particles by, for example, stirring the air. The mechanism by which the effect is caused is not fully clear, but it can be seen that the surface part of the fly ash particles is composed of oxidized metals and complex compounds. It is necessary to chlorinate the compound of However, the rate at which these types of compounds are chlorinated by Cl ₂ and HCl is generally dependent on the metal and Cl ₂
The reaction is significantly slower than the reaction with, and it is considered that this inhibits the progress of chlorination. In the method of the present invention, since roasting is performed while applying a shearing force to such particles, the compound layer on the surface is mechanically removed, the metal surface is exposed, and at the same time the oxide itself is finely divided. Was converted into
As a result, the rate of chlorination reaction is estimated to increase.

The fly ash can be roasted by a commonly used chlorination roasting furnace.
Generally, CO ₂ and H ₂ O are present in addition to O ₂ , and the atmosphere is oxidizing. The metal in the fly ash is easily converted to chloride by chlorine, but if the atmosphere has a strong oxidizing property, the chloride is oxidized in reverse. The reactivity of this oxidation reaction varies depending on the metal species. For example, the chloride of Pb is relatively stable, whereas the chloride of Fe is easily oxidized. The progress of such an oxidation reaction largely depends on conditions such as temperature and partial pressure of O _{2 in} the atmosphere. Therefore, in roasting fly ash as described above, the conditions such as the roasting temperature and the partial pressure of O _{2 in} the atmosphere can be adjusted as necessary to identify the metal components contained in the fly ash. It is also possible to selectively volatilize and separate only those as chlorides and leave other metals in the fly ash residue.

Next, the combustion gas containing the metal chloride volatilized and separated by roasting as described above is contacted with a liquid to be absorbed composed of water or an aqueous solution in a gas-liquid contacting device such as a scrubber, to be absorbed. It is dissolved and recovered in the recovery liquid. As the scrubber, various types such as a spray tower, a venturi scrubber, a Roto Kron N, an air tumbler, and a pea body scrubber can be used.

Since the combustion gas obtained by recovering and cleaning the metal chlorides as described above contains almost no harmful components such as Cl ₂ , it can be released into the atmosphere as it is. Recirculation to the roasting furnace is desirable for higher environmental safety.

Since the residue remaining after roasting is mainly composed of silicate and does not contain chlorine, heavy metals, etc., it can be used as aggregate, cement raw material, landfill disposal, stabilization treatment (pelletization), etc. Can be reused in any way. The recovery of the dissolved metal from the absorbing solution in which the metal chloride is dissolved as described above is performed as follows.

By passing through the above steps in the absorbing liquid, C
Since chlorides such as uCl ₂ , PbCl ₂ , ZnCl ₂ , and FeCl ₂ are dissolved, first, sulfuric acid is added to this absorbing solution to precipitate lead as PbSo ₄ , which is then recovered.
After adjusting H to 2 to 4, it is brought into contact with an iron piece to carry out cementation by utilizing a metal substitution reaction, and Cu is deposited and recovered on the surface of the iron piece. If the metal concentration is high,
It is also possible to recover the metal by electrolysis.

Fe and Fe are contained in the residual liquid after cementation.
And Zn are contained, H ₂ O₂ 2 values due to etc.
After oxidizing iron, first Ca (OH)₂ For example, PH is 4 to
Fe (OH) by adding about 6₃ To precipitate and filter
And Fe (OH)₃ Collect. Recovered Fe (O
H)₃ Is used as a flocculant, red iron oxide, ferrite, etc.
Is done.

Further, Zn and HCl are contained in the filtrate after the filtration.
Since it contains₂ CO ₃ For example, if the pH is
Add 8 to 10 to neutralize and add ZnCO₃ The precipitation
Let the filtered ZnCO₃ Collect. ZnCO₃ Haso
After that, it is refined by a known method and regenerated as metallic zinc.
Be done.

Finally, since the NaCl after neutralization is dissolved in the filtrate after the ZnCO ₃ filtration recovery, this is evaporated and concentrated to recover NaCl. The above has described the method of the present invention by taking the case of fly ash generated by incineration of shredder dust from scrapped automobiles and household electric appliances as an example, but the method for recovering metal from fly ash of the present invention is not limited to this. The same can be applied to the treatment of fly ash generated when waste is incinerated.
Further, in the above case, the case where the fly ash contains four metals of Fe, Zn, Pb, and Cu is exemplified, but of course,
Even if it does not contain a part of these, or even if it contains a metal other than these, the method of the present invention is applicable, as well as roasting fly ash, volatilizing and separating the metal as chloride to recover It is possible to recover each metal by applying a known metal recovery technique as appropriate after dissolving and recovering in a liquid.

[0022]

EXAMPLES The present invention will be specifically described below with reference to examples. Fly ash generated when fluidized and roasted shredder dust from an abandoned automobile at about 850 ° C was used as a sample. The metal content in this fly ash was as shown in Table 1.

First, the fly ash containing CaCl ₂ was allowed to stand in a heating furnace and heated to 700 ° C. As shown in Table 1, a considerable portion of the metal components contained in the fly ash was obtained. It was possible to recover the metal in the gas that volatilized and generated from the furnace. From these results, it was revealed that CaCl ₂ in the fly ash decomposed upon heating to generate chlorine gas and hydrogen chloride, and the metal volatilized as a chloride.

Based on the results of this test, in order to further increase the reaction efficiency of the metal, fuming and stirring were performed during roasting with chlorine.
As a result of heating at 750 ° C., as shown in Table 2, Cu, Pb
The volatility of Zn and Zn reached 90% or more. The volatilized metal chloride was recovered with a scrubber, diluted sulfuric acid was added to the obtained scrubbing solution to precipitate and recover PbSO ₄ , and after adjusting the pH to 3, iron pieces were added and cementation was performed as shown in Table 4. Cu with a quality of 80% was recovered. Further, since the solution after cementation contained Zn and Fe as shown in Table 3, first, H ₂ O _{2 was} added.
Is added to oxidize Fe (II) to Fe (III), and Ca is added to this.
(OH) 2 was added to adjust the pH to 6, and Fe (OH) ₃ precipitate and Zn solution were separated. Furthermore, the Zn solution contains Na ₂ CO
₃ was added for neutralization, ZnCO ₃ was precipitated, and filtered to recover ZnCO ₃ . The quality and recovery rate of the recovered Zn are as shown in Table 4. Finally, the filtrate after ZnCO ₃ filtration recovery contains almost no metal as shown in Table 3 and a large amount of NaCl dissolved as shown in Table 5. Recovered.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

[0029]

[Table 5]

[0030]

As described above, according to the present invention, Ca
Cl ₂ -containing fly ash as it is or recovered NaC
In order to recover the metal electrochemically after adding 1 and roasting while applying shearing force such as stirring to volatilize and separate the metal as chloride and dissolve this metal chloride in the liquid to be recovered. Not only can Cu, Zn, and Pb be recovered and removed from fly ash generated from municipal waste and shredder dust incineration facilities, but also detoxification of metals and chlorine can be performed. On the other hand, the fly ash residue can be directly landfilled or used as a cement raw material or the like. Therefore, according to the present invention, it is possible to separate and recycle the heavy metals and Cl in the fly ash, and it is expected that a high degree of resource reuse in the waste will be achieved.

Claims (2)

[Claims] 1. The chlorine generated by combustion of waste is Ca
A method for recovering metal from fly ash, which is fixed and contained as Cl ₂ , comprising: a) heating the fly ash in an oxidizing atmosphere while applying a shearing force to remove chlorine and hydrogen chloride generated by decomposition of CaCl ₂ ; Reacting with the metal components contained in the fly ash, b) contacting the absorbing solution with the metal chloride generated and volatilized to dissolve and recover, and c) separating the dissolved metal from the obtained recovery solution. A method for recovering metal from fly ash, which is characterized in that 2. In the step c), i) sulfuric acid is added to the recovery solution to precipitate lead as PbSO ₄ and recovered, and then the pH is adjusted to 2 to 4 and then contacted with an iron piece to precipitate Cu. Ii) Ca (OH) ₂ or CaCO ₃ is added to the residual liquid to precipitate Fe (OH) ₃ and then filtered to recover Fe, and iii) Na ₂ is added to the filtered liquid after filtration. CO ₃ is added to neutralize,
The method according to claim 1, wherein ZnCO ₃ is precipitated and filtered to recover Zn, and iv) the filtered filtered solution is concentrated by evaporation to collect NaCl.