JPH08117724A - Method of treating fly ash from incinerator or melting furnace - Google Patents

Abstract

(57) [Summary] [Purpose] From an incinerator or a melting furnace that can separate heavy metals and harmful substances contained in fly ash from an incinerator or a melting furnace in a safe form without using a cement solidification method or a melting treatment. To provide a method of treating fly ash. [Structure] First step of dissolving fly ash in water to adjust the pH to 3 to 7, and then separating the residue into a residue containing heavy metals and a filtrate containing soluble salts; repulping the residue to adjust the pH to lower than 3; A second step of eluting a heavy metal mainly composed of the above and fractionating it into a residue composed mainly of lead and a filtrate; neutralizing the filtrate obtained from the first and second steps to adjust to an alkaline side, zinc, A heavy metal hydroxide mainly composed of copper, and further, a sulfidizing agent is added to precipitate the remaining heavy metal which has not been converted into a hydroxide, and the precipitated heavy metal is separated into a final filtrate. It is characterized by comprising steps.

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 or a melting furnace in a municipal solid waste incinerator, an industrial waste incinerator, or the like.

[0002]

2. Description of the Related Art Generally, garbage discharged from business establishments and households (referred to as "urban garbage" or "general waste") is collected at an urban refuse incinerator and incinerated. At that time, cinders and fly ash generated from the incinerator are transported to the final disposal site and accumulated.

In addition to what is deposited as it is, heavy metals such as lead and cadmium contained in fly ash and harmful substances such as dioxins are solidified with cement and discarded, and cinders and fly ash are melted and solidified in a melting furnace. The landfill volume is also being reduced by using this method.

[0004]

However, in recent years, problems such as difficulty in securing a deposition site and harmful effects of heavy metals such as lead and cadmium contained in deposited fly ash and dioxins have been regarded as problems.

Therefore, a cement solidification method and a chemical treatment method have been developed and put into practical use in order to stabilize the above-mentioned harmful substances, but since the cement solidification method cannot reduce the landfill volume, there is a problem in securing a sedimentation site. The points remained unresolved. Although the elution of heavy metals contained in fly ash can be reduced by the kneading process of fly ash and cement (elution test according to the Environmental Agency Notification No. 13 method), this treatment method is not perfect and In addition to insufficient elution prevention efficiency, it is difficult to stabilize heavy metals in fly ash mixed with cement for a long time, considering the effect of acid rain.

On the other hand, there is a report that it is possible to reduce the volume and to make harmless by the thermal decomposition of dioxins by melting and treating the cinders and fly ash from the incinerator (Katsuya Nagata "Urban refuse incinerator" Status and Trends of Dioxin Countermeasures in Japan ", Journal of Japan Society of Waste, Vol. 3, No. 3).

However, according to the above-mentioned melting treatment, heavy metals such as lead and cadmium having a large vapor pressure are volatilized in the furnace, enter the exhaust gas, and are condensed in the exhaust gas treatment equipment to become fly ash again. was there.

Therefore, an object of the present invention is to remove heavy metals and harmful substances contained in fly ash from incinerators and melting furnaces in a stable form without solidifying or melting cement. To provide a method for treating fly ash.

[0009]

As a result of earnest research to achieve the above-mentioned object, the inventors of the present invention firstly dissolved fly ash in water to obtain p.
If H is adjusted to 3 to 7 and treated, the heavy metal component and the salt component in the fly ash can be separated by filtration, and the pH of the treatment liquid is adjusted to 3 in the subsequent step.
Control to a lower level to obtain a lead residue containing mainly lead, and a filtrate containing heavy metals and salts other than lead, and then neutralizing this filtrate easily and stably to remove water containing heavy metals mainly containing zinc. Oxidized starch is obtained, and these residues and starch can be utilized as resources for non-ferrous smelting, and pH
The inventors have found that the amount of the control mineral acid or neutralizing agent added is relatively small and can be evaluated in terms of cost.

That is, the present invention relates to a method for treating fly ash containing chlorine and sodium-based salts and zinc and copper-based heavy metals generated from an incinerator or a melting furnace, wherein the fly ash is dissolved in water. After adjusting the pH to be in the range of 3 to 7, solid-liquid separation is performed to separate a residue containing heavy metals and a filtrate containing salts from the first step; the resulting residue is repulped to pH 3 The second step in which the heavy metal containing zinc as a main component is eluted and the solid solution is separated into a lead residue containing lead as a main component and the filtrate, and the filtrate obtained in the first step and the second step Add a hydrating agent to precipitate the hydroxides of heavy metals consisting mainly of zinc and copper, and, if necessary, add a sulfiding agent to precipitate the remaining heavy metals that did not become hydroxides as sulfides. , A third step of filtering off these starches; There is provided a method of processing fly ash from incinerators or melting furnace, characterized in that Ranaru.

[0011]

In the first step of the present invention, fly ash is first dissolved in water to form a slurry, and a mineral acid such as hydrochloric acid or sulfuric acid is added to the slurry while stirring to adjust the pH to 3 to 7. Since the pH of the fly ash slurried varies depending on its composition, it is necessary to adjust the amount of mineral acid added according to the fly ash. If the pH of the slurry is already at the optimum pH, it is not necessary to add mineral acid. Further, the stirring time while maintaining the above pH may be at least about 10 minutes, and the temperature at that time may be room temperature. Then, the slurry is filtered to separate into a residue containing heavy metals and a filtrate containing salts.

In the second step, the residue obtained in the first step is repulped and hydrochloric acid is added to adjust the pH to a value lower than 3.0, preferably around 1.0 so that heavy metals other than lead are leached and dissolved. , A lead-based residue and a filtrate containing dissolved heavy metal components such as zinc and salts such as calcium and chlorine. In addition, it is important to utilize the residue obtained by removing the leachate adhering to the residue in the above filtration as a resource, and normal washing with water is also possible, but washing with a sodium hydroxide solution can recover lead residues with few impurities. Sometimes,
It is preferable as a raw material for lead smelting.

In the third step, after mixing the filtrates generated in the first and second steps, at least one of sodium hydroxide, sodium carbonate or calcium hydroxide is added as a neutralizing agent to adjust the pH to 7.0. More preferably 7.5 to
By adjusting to 8.5, a heavy metal mainly containing zinc is generated as a hydroxide, and when a small amount of heavy metal remains in the solution, sodium sulfide, sodium hydrosulfide, hydrogen sulfide, etc. A sulfiding agent is added to precipitate the remaining heavy metal as a sulfide, which is separated by filtration to obtain a zinc starch and a final neutralized filtrate.

Therefore, according to the method of the present invention, the heavy metal contained in the fly ash is mainly a lead-containing residue, and mainly zinc.
Since it can be recovered separately from hydroxides and sulfides containing copper, cadmium or mercury, they can be used as non-ferrous smelting raw materials.

[0015]

EXAMPLE FIG. 1 is a flow sheet of the processing steps used in this example, and the present invention will be explained in more detail with reference to this figure, but the scope of the present invention is limited by the following examples. It is not something that will be done.

(1) First, 2 liters of distilled water was placed in a 3 liter beaker, and 100 g of fly ash from the incineration plant A having the composition shown in Table 1 was added to the slurry to make a slurry, and the mixture was stirred for 10 minutes. It was .4. Next, this slurry was filtered to separate it into a residue and a filtrate. Heavy metal components in fly ash were separated into a residue, and soluble salts such as sodium and chlorine were separated into a filtrate (the above first step).

(2) Next, hydrochloric acid is added to the residue obtained by repulping the residue with 2 liters of distilled water and adjusting the pH so that the pH becomes 1.0, followed by stirring for 10 minutes, and the obtained lead residue is subjected to solid-liquid separation. And separated into a lead residue and a filtrate. Rather than using water as a means for cleaning this lead residue, sodium hydroxide (NaO
It was found that the use of the (H) solution is more effective in removing impurities other than lead (the above is the second step).

(3) Next, after mixing the filtrate obtained in the second step and the filtrate in the first step, an aqueous sodium hydroxide solution having a concentration adjusted to 200 g / l was added to adjust the pH to 7.0.
Sodium hydrosulfide (NaHS) solution neutralized to 10 g / l and adjusted to a redox potential of -100 mV (A
g / AgCl electrode) to produce a hydroxide precipitate of heavy metal mainly containing zinc and a sulfide precipitate of other heavy metal, and solid-liquid separation is performed to separate a residue and a final filtrate. It was washed to obtain zinc starch (above third step).

Regarding the lead residue obtained from the lead starch as described above, the zinc starch, and the neutralized filtrate in the final step, P
The contents of b, Zn, Fe, Cu, Si, Al, Na and Cl were examined, and the results are shown in Table 1 together with the contents of the respective components of the fly ash.

[0020]

[Table 1]

As can be seen from the results in Table 1, heavy metals such as lead and zinc contained in the fly ash were separated almost completely in a stable form. The lead quality in the lead residue is 31.23%,
The zinc grade in the zinc starch is 34.05%, which can be treated as a resource in a non-ferrous smelter, and the final neutralization filtrate is below the wastewater standard, so that it can be directly fed to rivers or the sea. It could be released.

[0022]

As described above, according to the method of the present invention, heavy metals contained in fly ash can be separated in a stable form, and the separated lead-containing residue and zinc are mainly contained. Since the heavy metal aquatic sediments that utilize lead and zinc can be used as resources, safe disposal can be performed without landfilling harmful heavy metals in the repository.

[Brief description of drawings]

FIG. 1 is a flow sheet showing processing steps used in an example of the present invention.

Front page continuation (72) Inventor Satoshi Sugizawa 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd.

Claims (2)

[Claims] 1. Chlorine generated from an incinerator or a melting furnace,
In a method for treating fly ash containing salts containing sodium as a main component and heavy metals containing zinc, copper and lead as a main component, the fly ash is dissolved in water to adjust the pH to a range of 3 to 7. First step of solid-liquid separating into a residue containing heavy metals and a filtrate containing salts; repulping the obtained residue and adjusting the pH to a value lower than 3 to elute heavy metals mainly containing zinc, Second step of solid-liquid separation into a lead residue containing lead as a main component and a filtrate; Next, a neutralizing agent is added to the filtrate obtained in the first step and the second step to remove heavy metals mainly containing zinc and copper. A method for treating fly ash from an incinerator or a melting furnace, which comprises a third step of precipitating a hydroxide, solid-liquid separating it into a precipitate and a filtrate. 2. Chlorine generated from an incinerator or a melting furnace,
In a method for treating fly ash containing salts containing sodium as a main component and heavy metals containing zinc, copper and lead as a main component, the fly ash is dissolved in water to adjust the pH to a range of 3 to 7. First step of solid-liquid separating into a residue containing heavy metals and a filtrate containing salts; repulping the obtained residue and adjusting the pH to a value lower than 3 to elute heavy metals mainly containing zinc, Second step of solid-liquid separation into a lead residue containing lead as a main component and a filtrate; Next, a neutralizing agent is added to the filtrate obtained in the first step and the second step to remove heavy metals mainly containing zinc and copper. A third step of precipitating the hydroxides, further adding a sulfiding agent to precipitate the remaining heavy metals not converted into hydroxides as sulfides, and filtering these precipitates off; A method for treating fly ash from an incinerator or melting furnace.