JP2006131962A - Method for separating and recovering heavy metal contained in molten flying ash - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for volatilize-separating or wash-separating lead, zinc and copper contained in molten flying ash by heating pellet of the molten flying ash. <P>SOLUTION: The molten flying ash is granulated to make the pellet of the molten flying ash, and eutectic mixture having two or more components among CaCl<SB>2</SB>, NaCl and KCl, is generated by heating the above pellet at 800-1100°C and also, lead oxide contained in the eutectic mixture and the pellet is chlorinate-reacted to make lead chloride, or unburnt carbon dust and iron oxide, zinc oxide contained in the pellet are reduction-reacted and the respective materials are volatilized and separated as a single zinc, or the unburnt carbon and copper oxide contained in the pellet are reduction-reacted and a single copper is generated, and this pellet is washed with water and soluble components are removed, and the residue of the pellet containing the single copper is recovered. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of separating and recovering heavy metals such as lead contained in molten fly ash, and more particularly to a method of recovering by separating and recovering heavy metals by volatilization or heating after heating.

The melt-solidification process is widely applied to various wastes because it has the advantage of being excellent in volume reduction of waste and being able to effectively use molten slag as a resource. On the other hand, the melting and solidifying treatment generates molten fly ash containing heavy metals that are harmful to the human body and the natural ecosystem. Although molten fly ash contains heavy metals similar to crude ore, inorganic chlorinated compounds such as NaCl, KCl, and CaCl ₂ are the main components, so it is difficult to reduce Yamamoto to non-ferrous smelting. Has been disposed of in landfills after stabilization of heavy metals. However, it is included in molten fly ash due to the recent depletion of landfill sites and the reduction of metal resources (Pb: 21 years, Zn: 20 years, Cu: 39 years). A technique for separating and recovering heavy metals from NaCl, KCl, and CaCl ₂ has been desired.

For the above problem, for example, as a method for recovering metal from fly ash containing chlorine generated by combustion of waste as CaCl ₂ , fly ash is heated in an oxidizing atmosphere while applying shearing force, There has been proposed a method for recovering heavy metals by reacting chlorine and hydrogen chloride generated by the decomposition of CaCl ₂ with metal components contained in fly ash (Japanese Patent Laid-Open No. 8-35018).
Also, a mixing step of mixing a waste containing at least zinc in an oxide state and a reducing agent having a particle size of 200 μm or less, and a granulated product so that the shortest distance from the center to the surface of the mixture is 25 mm or less A zinc oxide-containing waste comprising: a granulating step for producing a product; and a zinc recovery step for heating the granulated product under vacuum to reduce zinc oxide and to collect zinc by evaporation A processing method for an object has been proposed (Japanese Patent Laid-Open No. 2002-206123).
Furthermore, as a method for efficiently separating and recovering difficult-to-separate heavy metals from solid waste, the solid waste is halogenated in a temperature field of 250 ° C. or lower in the presence of a halogenating agent, and the generated heavy metal halide is recovered. A method for separating and recovering difficult-to-separate heavy metals, characterized by carrying out volatile separation in a temperature field of 250 to 900 ° C., has been proposed (Japanese Patent Laid-Open No. 2002-275550).

Japanese Patent Laid-Open No. 08-35018 JP 2002-206123 A JP 2002-275550 A

However, the method for recovering metal from fly ash described in Japanese Patent Application Laid-Open No. 08-35018 uses a chloride reaction with metal using CaCl ₂ alone, but the chlorine source contained in molten fly ash In addition to CaCl ₂ , it contains a component that undergoes a chlorination reaction with metals such as NaCl and KCl. Therefore, in the method described in Japanese Patent Application Laid-Open No. 08-35018 that does not utilize these NaCl and KCl, the recovery efficiency of heavy metals is poor.

  In addition, when the organic waste treatment method described in JP-A-2002-206123 is applied to molten fly ash, the low melting point inorganic chlorine compound (melting point: NaCl ( 801 ° C.) and KCl (770 ° C.) are also volatilized together with zinc, resulting in a recovered product in which impurities are mixed.

  Furthermore, in the method for separating and recovering difficult-to-separate heavy metals described in JP-A No. 2002-275550, a separate halogenating agent is required, and adding a halogenating agent to a solid waste Since it is necessary to install an anti-corrosion and acid gas treatment facility, it is necessary to operate in a form in which the addition amount of the halogenating agent is suppressed as much as possible. As a result, there is a problem that the recovery efficiency of the hardly separable metal is poor.

  The present invention has been made in view of the above-mentioned problems, and does not add a new chlorine agent and does not require countermeasures against corrosion. It is an object of the present invention to provide a method for recovering heavy metals from molten fly ash that can be recovered in this manner.

In order to achieve the above object, the method for separating and recovering heavy metals contained in molten fly ash in the present invention comprises the steps of granulating the molten fly ash to produce a granulated product of the molten fly ash, and the granulation By heating the product at 800 to 1100 ° C., a eutectic mixture containing any two or more of CaCl ₂ , NaCl and KCl contained in the granulated product is formed, and the eutectic mixture and the aforesaid granulated product are produced. And a step of subjecting lead oxide contained in the granules to a chlorination reaction to volatilize and separate as lead chloride.
As a result, the lead component in the molten fly ash can be separated and recovered with high efficiency without adding an additive or the like.

Further, the method for separating and recovering heavy metals contained in the molten fly ash in the present invention comprises a step of granulating the molten fly ash to produce a granulated product of the molten fly ash, and the granulated product at 800 to 1100 ° C. And a step of subjecting unburned carbon and iron oxide contained in the granulated product to a reduction reaction of zinc oxide and volatile separation as simple zinc.
Thereby, the zinc content in the molten fly ash can be separated and recovered with high yield.

Furthermore, the method for separating and recovering heavy metals contained in the molten fly ash in the present invention comprises a step of granulating the molten fly ash to produce a granulated product of the molten fly ash, and the granulated product at 800 to 1100 ° C. A step of reducing the unburned carbon and copper oxide contained in the granulated product by a reduction reaction to produce simple copper, and washing the granulated product after heating with water. And a step of removing a dissolved component and recovering a residue of a granulated product containing simple copper.
Thereby, it can be effectively utilized by collecting the residue of the granulated material as a copper-containing material.

Further, the method for separating and recovering heavy metals contained in the molten fly ash in the present invention comprises a step of granulating the molten fly ash to produce a granulated product of the molten fly ash, and the granulated product at 500 to 750 ° C. And a step of generating a eutectic mixture containing any two or more of CaCl ₂ , NaCl and KCl contained in the granulated product, and the heated granulated product at 850 to 1100 ° C. And a step of subjecting the eutectic mixture and lead oxide contained in the granulated product to a chlorination reaction to volatilize and separate as lead chloride.

As is clear from the above description, the present invention can volatilize and separate lead oxide and zinc oxide in molten fly ash only by heating without using a new chlorine agent.
Further, the residue of the granulated product after heating and washing with water can be recycled as a single copper-containing material, which can contribute to a reduction in the amount of landfill disposal. Furthermore, it is not necessary to take measures against the corrosion of the apparatus with respect to the addition of the chlorine agent and the acid gas treatment against the volatilization of the unreacted chlorinating agent, and the treatment process can be simplified.

As a result of intensive studies by the present inventors, lead oxide present in the molten fly ash reacts with a eutectic mixture containing any two or more of CaCl ₂ , NaCl and KCl contained in the molten fly ash. It was found that volatile separation can be achieved by becoming lead chloride (PbCl ₂ melting point: 501 ° C., boiling point: 950 ° C.). That is, as shown in FIG. 1, the present inventor calculated the average value (Average (1)), 1/2 of the result of simulated fly ash in which 1.0 equivalent each of NaCl and KCl reagents was added to the PbO reagent. Average value of simulated fly ash (Sample (2)) added by mixing each equivalent amount of NaCl and KCl reagents, and the result of simulated fly ash added by 1.0 equivalent each of CaCl ₂ , NaCl and KCl reagents (Average) (3)) Simulated fly ash (Sample (4)) to which 1/3 equivalent of CaCl ₂ , NaCl, and KCl reagent were mixed and added was examined and compared. As a result, the volatilization rate of lead was higher when the CaCl ₂ , NaCl, and KCl reagents were mixed than the average value when the CaCl ₂ , NaCl, and KCl reagents were added individually (Average (1), (3)). (Sample (2), (4)) was found to obtain a high volatility.

In addition, regarding volatile separation of zinc oxide and copper oxide from molten fly ash, it was difficult to become a metal chloride depending on the eutectic mixture of CaCl ₂ , NaCl and KCl contained, but instead zinc contained in molten fly ash. Zinc oxide is converted into simple zinc (Zn) by unburned carbon (C) and iron oxide (Fe ₂ O ₃ ).
When the melting point is 419.6 ° C., the boiling point is 907 ° C., the volatile separation is achieved. The copper oxide is converted into a single copper (Cu melting point: 1083.4 ° C. by reduction with unburned carbon).
(Boiling point: 2570 ° C.), and found to remain in the molten fly ash.

ZnO + C → Zn + CO (1)
Fe ₂ O ₃ + 3C → 2Fe + 3CO (2)
ZnO + Fe → Zn + FeO (3)
CuO + C → Cu + CO
(4)

In the present invention, “molten fly ash” refers to municipal waste, automobile shredder dust (ASR), medical waste, sewage sludge, construction waste, waste tires, waste plastic, waste solid fuel (RDF), and incineration ash thereof. Those that have been melted and solidified are also included. The heavy metal content in the molten fly ash is preferably 10,000 mg / kg or more in terms of a simple substance, and if the content is less than that, a recovered material with sufficient quality cannot be obtained even if heating is performed.
It is desirable that the inorganic chlorine compound (NaCl, KCl, CaCl ₂ ) in the molten fly ash is contained in an amount of 1.0 equivalent or more in terms of the amount of Cl necessary for the chlorination reaction of lead oxide. When the content is less than that, it is necessary to input a chlorine source from the outside.

Moreover, it is desirable that the unburned carbon content in the molten fly ash is 5.0 wt% or more. In the case of a lower content, the unburned carbon content in the molten fly ash is 5.0 wt% or more. It is desirable to add a carbon raw material so that Here, examples of the “carbon raw material” include pulverized coal, powdered coke, activated carbon, charcoal, bamboo charcoal and the like, but solid waste may be used as long as it contains carbon, for example, molten fly ash with a large amount of unburned carbon. It is also possible to mix.

When heating the molten fly ash, the molten fly ash is a fine particle having a particle diameter of about 1 to 100 μm, so that there is a problem that it is easy to generate dust and it is difficult to perform efficient heating. Therefore, it is necessary to add molten fly ash in the form of fine particles to a humidifying kneader, add water, and make the humidified molten fly ash into a granulated product having a particle size of 10 to 50 mm using a granulator. . In consideration of the time required for the reaction between the inorganic chlorine compound, unburned carbon and iron oxide, and the heavy metal, the time for heating this granulated product with a heat treatment apparatus may be 60 to 180 minutes. preferable.

As for the heating temperature, generation of the eutectic mixture containing any two or more of CaCl ₂ , KCl and NaCl is started from around 550 ° C. to about 850 ° C., but was generated from around 750 ° C. Chlorination reaction between the eutectic mixture and heavy metals also begins to occur. Therefore, in order to simultaneously perform the formation of the eutectic mixture and the chlorination reaction between the eutectic mixture and the heavy metal, it is preferable to heat in the range of 800 to 1100 ° C. The molten fly ash granulated product charged into the heat treatment apparatus is heated by hot air gas, and lead oxide and zinc oxide in the granulated product are volatilized and separated. As the hot air gas used in the heat treatment apparatus, air, nitrogen gas, combustion exhaust gas, or the like can be used, but it is more preferable to use nitrogen gas because dioxin may be re-synthesized.

Volatilized lead oxide and zinc oxide are collected by a collecting device such as a bag filter. The collection temperature is desirably 200 ° C. or lower because it is desirable that lead oxide and zinc oxide are completely condensed. On the other hand, the residue of the molten fly ash granulated material from which lead oxide and zinc oxide have been separated is discharged from the heat treatment apparatus in order to prevent re-synthesis of dioxins, and then is put into a water washing treatment facility and rapidly cooled. Then, the residue is washed with water to separate a soluble component (inorganic chlorine compound) and an insoluble component (single copper) in the residue to recover a residue containing copper. In the present invention, “soluble component” means NaCl, KCl, CaCl ₂ which are inorganic chlorine compounds, and “insoluble component” means single copper.

The present invention will be described in more detail by the following embodiments. FIG. 2 is a schematic diagram of an apparatus for carrying out the method according to the present invention. This apparatus includes a granulator 1 for granulating humidified molten fly ash, a heating furnace 2 for heating and separating lead oxide and zinc oxide contained in the granulated product, and lead oxide separated by volatilization. , A collecting device 3 for collecting zinc oxide, and a washing device 4 for washing the residue of the granulated product after the lead oxide and zinc oxide are volatilized and separated.

The method according to the present invention is performed, for example, as follows. The molten fly ash is pre-humidified with water and kneaded by a kneader (not shown), and the molten fly ash is put into the granulator 1 and the humidified and kneaded molten fly ash has a predetermined particle size (10 to 50 mm). Granulate into granules.
This is to improve the ventilation of the hot air gas in the heating furnace and to prevent the generation of secondary fly ash (dust). Thereafter, the granulated material is put into the heating furnace 2 and heated at a predetermined temperature (for example, 900 ° C.) for a predetermined time (for example, 120 minutes) by hot air blown from the lower part of the heating furnace. By this heating, lead oxide contained in the granulated material is volatilely separated as lead chloride (PbCl ₂ ) and zinc oxide as simple zinc (Zn). These volatiles are collected by the collection device 3 installed in the subsequent stage.
On the other hand, the residue of the granulated product after heating to separate lead oxide and zinc oxide is put into the water washing device 4 and rapidly cooled. In the water washing apparatus 4, soluble components (NaCl, KCl, CaCl ₂ ) in the residue are removed, and the residue containing concentrated single copper is recovered.

Examples are shown below. 3 to 5 show lead when molten fly ash (A: municipal waste incineration ash, B: ASR, C: municipal waste) generated from three different molten raw materials is heated at 600 to 900 ° C for 120 minutes. The relationship between the volatility of zinc, copper and the heating temperature is shown. From this result, it can be seen that lead can be almost volatilized and separated at a temperature of 850 ° C. or higher for any of the molten fly ash A, B, and C (FIG. 3). As for zinc, it can be seen that the volatilization rate improves with increasing heating temperature for each of the molten fly ash A, B, and C. (FIG. 4).

Here, with regard to the molten fly ash B having an unburned carbon content of 9.56%, 100% volatile separation was possible at a heating temperature of 800 ° C. or higher, but the molten fly ash A (unburned carbon content 3 .66%) and molten fly ash C (unburned carbon content: 2.31%) could not sufficiently evaporate zinc. Therefore, the molten fly ash C with a small amount of unburned carbon was heated using the molten fly ash C ″ added with a carbon reagent so that the carbon content was 9.56%. It was confirmed that the volatilization rate was the same as that of the fly ash B. In addition, with regard to copper, almost no improvement in volatilization rate was observed for all of the molten fly ash A, B, and C, and it remained on the residue side. Was confirmed (FIG. 5).

  Since the present invention relates to a method capable of recovering lead oxide, zinc oxide and copper oxide contained in molten fly ash as a compound or a simple substance, the industrial applicability is great.

It is the figure which showed the relationship between the containing form of the inorganic chlorine compound in simulated fly ash, and lead volatilization rate. It is an apparatus schematic diagram for implementing the method of this invention. It is the figure which showed the relationship between lead volatilization rate and heat processing temperature. It is the figure which showed the relationship between zinc volatilization rate and heat processing temperature. It is the figure which showed the relationship between copper volatilization rate and heat processing temperature.

Explanation of symbols

1 Granulator 2 Heating furnace 3 Collection device 4 Flushing device

Claims (5)

A method for separating and recovering heavy metals contained in molten fly ash,
A step of granulating the molten fly ash to produce a granulated product of the molten fly ash;
By heating the granulated product at 800 to 1100 ° C., a eutectic mixture containing any two or more of CaCl ₂ , NaCl and KCl contained in the granulated product is formed, and the eutectic mixture And a step of subjecting lead oxide contained in the granulated product to a chlorination reaction to volatilize and separate as lead chloride. A method for separating and recovering heavy metals contained in molten fly ash, comprising: A method for separating and recovering heavy metals contained in molten fly ash,
A step of granulating the molten fly ash to produce a granulated product of the molten fly ash;
Heating the granulated product to 800-1100 ° C. to cause a reduction reaction between unburned carbon and iron oxide and zinc oxide contained in the granulated product, and volatilizing and separating as single zinc. A method for separating and recovering heavy metals contained in molten fly ash. A method for separating and recovering heavy metals contained in molten fly ash according to claim 2,
A method for separating and recovering heavy metals contained in molten fly ash, wherein the content of unburned carbon contained in the granulated product is 5.0 wt% or more. A method for separating and recovering heavy metals contained in molten fly ash,
Granulating the molten fly ash to create a granulated product of the molten fly ash;
Heating the granulated product at 800 to 1100 ° C. to reduce the unburned carbon and copper oxide contained in the granulated product to produce simple copper,
Washing the granulated product after heating to remove soluble components in the granulated product, and recovering the residue of the granulated product containing simple copper, For separating and recovering heavy metals contained in A method for separating and recovering heavy metals contained in molten fly ash,
A step of granulating the molten fly ash to produce a granulated product of the molten fly ash;
Heating the granulated product at 500 to 750 ° C. to produce a eutectic mixture containing two or more of CaCl ₂ , NaCl and KCl contained in the granulated product;
Heating the granulated product heated at 850 to 1100 ° C. to cause the eutectic mixture and lead oxide contained in the granulated product to undergo chlorination reaction to volatilize and separate as lead chloride. A method for separating and recovering heavy metals contained in molten fly ash.