JP3300081B2 - Method for treating fly ash from incinerators and melting furnaces - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating heavy metal-containing fly ash generated from an incinerator and a melting furnace in a municipal waste incineration plant, an industrial waste incineration plant, or the like.

[0002]

2. Description of the Related Art Generally, garbage (called "municipal garbage" or "general waste") discharged from business establishments and households is collected at municipal garbage incineration plants and incinerated. At that time, cinders and fly ash generated from the incinerator had been deposited at the final disposal site.

[0003] In recent years, however, problems have been raised in terms of difficulty in securing a deposition site and the harmful effects of heavy metals such as lead and cadmium and dioxins contained in fly ash to be deposited.

For this reason, a cement solidification method and a chemical treatment method have been developed and put into practical use in order to stabilize the harmful substances. However, according to the cement solidification method, the landfill volume cannot be reduced. The issue of security remained unresolved. It has been reported that the kneading of fly ash and cement eliminates the elution of heavy metals contained in fly ash (dissolution test according to the Environment Agency Notification No. 13 method). In the case of fly ash, heavy metals in fly ash kneaded with cement were not always stable (Takeshi Kikuchi, "Detoxification of incineration residues by melting treatment of garbage incineration ash by plasma and generation of slag Recycling "PPM1992 / 5).

[0005] On the other hand, there is a report that melting and treatment of cinders and fly ash from an incinerator can reduce the volume and detoxify the dioxins by thermal decomposition (Katsuya Nagata, "Urban garbage incinerator"). Current Status and Trends of Dioxin Countermeasures in Japan, "Journal of the Society of Waste Management, Vol.

However, according to the above melting treatment, heavy metals such as lead and cadmium having a high vapor pressure are volatilized in the furnace and enter the exhaust gas, and the heavy metals entering the exhaust gas are condensed in the exhaust gas treatment facility and fly again. There was a problem of becoming ash.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention solves the above-mentioned problems of the prior art and provides an incinerator and a melting furnace capable of separating heavy metals contained in fly ash in a stable manner. It is an object of the present invention to provide a method for treating fly ash.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, leached fly ash at a pH of 3 or less, filtered off the residue, and added a neutralizing agent and a sulfurizing agent. Then, it was found that the above problem was solved by filtering off the generated precipitate, and the present invention was reached.

That is, the present invention is a method for treating fly ash containing sodium and potassium generated from incinerators and melting furnaces and heavy metals such as iron, zinc, copper and lead. A first step of adding a mineral acid such as hydrochloric acid or sulfuric acid and dissolving at a pH of 3 or less to elute heavy metals other than lead and filtering out a residue containing lead. At least one oxidizing agent selected from the group consisting of hydrogen water, sodium hypochlorite and chlorine gas is added to oxidize iron dissolved in the filtrate, and then sodium hydroxide, sodium carbonate or calcium hydroxide, etc. A neutralizing agent is added to neutralize the filtrate to a pH in the range of 3 to 5 to form an iron hydroxide precipitate, and the second step of filtering off the precipitate; and A neutralizing agent such as sodium hydroxide, sodium carbonate or calcium hydroxide is added to the filtrate obtained in the above step to neutralize the solution to a pH of 7 or more to form a heavy metal hydroxide mainly composed of zinc. According to a third step of adding a sulfurizing agent such as sodium sulfide, sodium hydrosulfide or hydrogen sulfide to the filtrate to precipitate the remaining heavy metals as sulfides, and filtering out these precipitates. The present invention provides a method for treating fly ash from incinerators and melting furnaces.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention will be specifically described with reference to an example of a method for treating fly ash generated during melting treatment of incinerated ash in a municipal garbage incineration plant.

First, fly ash is dissolved in water to form a slurry, and a mineral acid (inorganic acid) such as hydrochloric acid or sulfuric acid is added to the slurry while stirring to adjust the pH to 3 or less. Since the pH of fly ash varies depending on its composition, the amount of mineral acid added needs to be adjusted according to the pH of fly ash. In other words, the lower the pH of the slurry, the higher the lead quality of the lead residue obtained later tends to be. Therefore, the optimum pH is set according to the quality of fly ash, etc., and the amount of the mineral acid added is adjusted to obtain the pH. You just have to do it. In addition, p of the above slurry
If H is already at the optimum pH, no mineral acid needs to be added. Further, the stirring time for maintaining the above pH may be at least 10 minutes, and the temperature at that time may be room temperature.

Next, the slurry is filtered to separate into a residue containing lead and an aqueous solution containing heavy metals other than lead.
In addition, in order to remove the leachate adhering to the residue in the above-mentioned filtration, it is necessary to sufficiently wash with water, and this operation is particularly important when the obtained residue is used as a resource.

The filtrate obtained as described above generally contains cadmium, copper, iron, etc. in addition to zinc, but when fly ash contains a large amount of iron, it is obtained in a later step. It is necessary to selectively separate iron because the zinc quality in the precipitate of heavy metal mainly composed of zinc is lowered.

Therefore, in the method of the present invention, when the fly ash contains a large amount of iron, the filtrate is selected from the group consisting of oxidizing agents (hydrogen peroxide, sodium hypochlorite, chlorine gas, etc.). At least one) to oxidize ferrous ions dissolved in the solution to ferric ions, and then neutralize by adding a neutralizing agent such as caustic soda to reduce ferric ions to water. Iron is selectively separated by precipitating it as an oxide and filtering this precipitate off.

Next, zinc is mainly added to the filtrate from which lead and iron have been removed by adding a neutralizing agent such as sodium hydroxide, sodium carbonate or calcium hydroxide to adjust the pH thereof to 7 or more. If heavy metal remains in the solution, a sulfurizing agent such as sodium sulfide, sodium hydrosulfide, or hydrogen sulfide is added to the solution to remain. The heavy metals are precipitated as sulfides and the solution is filtered to obtain zinc deposits and a neutralized filtrate.

As described above, in the method of the present invention, heavy metals contained in fly ash are converted into residues (mainly containing lead), hydroxides (mainly containing zinc), and sulfides (mainly (Contains heavy metals other than lead and zinc). Therefore, the residue containing mainly lead and the hydroxide of heavy metals mainly containing zinc can be used as resources of non-ferrous metals.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited by the following examples.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the method for treating fly ash according to the present invention will be described below.

First, 2 g of distilled water was put into a 3 liter beaker, and 100 g of fly ash was put into the slurry with stirring. The slurry at this time had a pH of 3, so that a slurry was added without adding a mineral acid such as hydrochloric acid. Stirring was performed for minutes. Next, this slurry was filtered to separate into a residue and a filtrate, sodium hypochlorite was added to the obtained filtrate, and an aqueous solution of sodium hydroxide adjusted to a concentration of 200 g / l was added to neutralize to pH5. Then, iron was precipitated as hydroxide and separated by filtration.

Next, an aqueous sodium hydroxide solution is added to the filtrate obtained by filtering the precipitate containing iron until the pH of the filtrate becomes 7, and the aqueous sodium sulfide solution adjusted to a concentration of 5 g / l is further oxidized. It was added until the reduction potential reached 0 mV to form a zinc hydroxide-based heavy metal hydroxide precipitate and other heavy metal sulfide precipitates.

Next, the solution in which the precipitate was formed was filtered, and separated into a zinc residue and a neutralized filtrate (FIG. 1). The chemical used for the above neutralization and the like was adjusted to a concentration that allows easy addition.

Pb, Z in the residue, iron deposit, precipitate (zinc deposit), neutralized filtrate and fly ash obtained as described above
The contents (ratio) of n, Fe, Cd, Na ₂ O, K ₂ O and Cl were examined, and the results are shown in Table 1.

[0023]

[Table 1]

As can be seen from Table 1, heavy metals such as lead and zinc contained in fly ash were almost completely separated in a stable manner. The lead grade in the residue was 40.2%, and the zinc grade in the precipitate was 44.4%, which could be treated as a resource at a non-ferrous smelter. Further, a dissolution test was conducted on the iron palace according to the Environment Agency Notification No. 13, and the dissolution test satisfies the criteria and was found to be landfilled in a controlled final disposal site. Furthermore, the neutralized wastewater was below the wastewater standard and could be discharged directly into rivers and the sea.

[0025]

According to the development of the method of the present invention, heavy metals contained in fly ash can be separated in a stable manner. In addition, the residue containing lead separated by the method of the present invention and the hydroxide of heavy metal mainly containing zinc can be used as a resource of lead and zinc, so that the harmful heavy metal is not reclaimed. Safe disposal can be performed.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of the method of the present invention.

Continued on the front page (72) Inventor, Hisashi Sasaki, 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Kenichi Matsuura 1-8-2, Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Toru Nishiyama 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (56) References JP-A-4-265189 (JP, A) JP-A-61-171583 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B09B 3/00

Claims (1)

(57) [Claims] 1. A method for treating fly ash containing sodium and potassium generated from an incinerator and a melting furnace and heavy metals such as iron, zinc, copper and lead, wherein the fly ash is used as it is or a mineral acid is added. Then, a heavy metal other than lead is eluted by dissolving at pH 3 or less, a first step of filtering out a residue containing lead, and the filtrate obtained in the first step is subjected to a hydrogen peroxide solution, sodium hypochlorite and By adding at least one oxidizing agent selected from the group consisting of chlorine gas, oxidizing iron dissolved in the filtrate, and then adding a neutralizing agent, and neutralizing the filtrate to a pH in the range of 3 to 5. A second step in which a hydroxide of iron is formed and the precipitate is filtered off, and a neutralizing agent is added to the filtrate obtained in the second step, and the mixture is neutralized to pH 7 or more to mainly contain zinc. Heavy metal hydroxide An incinerator and a melting furnace, comprising a third step of adding a sulfurizing agent to the filtrate, if necessary, to precipitate the remaining heavy metals as sulfides, and filtering off these precipitates. For processing fly ash