JPS63111990A - Treatment for stabilizing heavy metals in flying cinder of refuse incineration - Google Patents

Abstract

PURPOSE:To eliminate generation of a trouble by elution of heavy metal ions, etc., in a reclaimed land, etc., by adding a sulfurizing agent and a proper volume or water to the flying cinders of refuse incineration and kneading the cinders to convert the heavy metals contained in the flying cinders to hardly soluble sulfide, thereby stabilizing the cinders. CONSTITUTION:The sulfurizing agent and a proper volume of water are added to the flying cinders of refuse incineration and the cinders are kneaded to convert the heavy metals contained in the cinders to the hardly soluble sulfide, by which the cinders are stabilized. Namely, this method is greatly effective for the prevention of environmental pollution and the expansion of the range for utilizing the flying cinders like; for example, the troubles by the elution of the heavy metal ions, etc., in the reclaimed land, etc., for the treated matter of the above-mentioned flying cinders are eliminated and the treated cinders are safely usable.

Description

[Detailed Description of the Invention] "Object of the Invention" (Industrial Field of Application) The present invention relates to a stabilization treatment method for converting heavy metals contained in waste incineration fly ash into compounds that are difficult to elute.

(Prior art) In recent years, most of the general waste, municipal waste, industrial waste, remains of animals and plants, various sludge, etc. generated in cities are incinerated in incinerators, and the amount of fly ash generated is increasing year by year. The number of pollutants is increasing, and how to deal with it has become a major problem in urban environmental administration. In general, fly ash contains heavy metals that are harmful to the human body, and they exist in the form of stable oxides and other soluble salts such as chlorides and sulfates. It cannot be disposed of as a landfill, and even if it is solidified with cement, lead and other substances may leach out and cause problems.

Conventionally adopted methods for stabilizing heavy metals include JP 53-12772, in which an acidic solution is added to fly ash to dissolve heavy metals and filtered, and an iron salt is added to the solution to cause a ferrite production reaction. A method for separating heavy metals by incorporating them into ferrite precipitate crystals, ■ JP-A-54-161583 Water is added to fly ash to elute heavy metals, and sodium hydroxide is added to this to precipitate the heavy metals as hydroxides. Method of filtering slurry of lettuce and sintering and solidifying the residue, ■ Japanese Patent Publication No. 60-52876
There is a method in which acid is added to fly ash to dissolve heavy metals and then filtered, this solution is treated with alkali or sulfide to precipitate heavy metals, which is filtered, and the residue is melted and solidified. However, these methods require complicated processing steps such as filtration or sintering and solidification, and have the disadvantage that the processing cost is very high. There were concerns that salts would need to be discharged and this would cause secondary pollution.

(Problems to be Solved by the Invention) The present invention was devised in view of the current situation, and provides a method for preventing the elution of heavy metals using an inexpensive treatment agent and in a simple treatment process. The purpose is to

``Structure of the Invention'' (Means for Solving the Problems) The present invention involves adding a sulfurizing agent and an appropriate amount of water to waste incineration fly ash and kneading the mixture to convert the heavy metals contained in the fly ash into hardly soluble sulfides. The method is a method for stabilizing heavy metals in waste incineration fly ash, which is characterized by converting and stabilizing the heavy metals into ash.

(Function) In the present invention, it is necessary to convert the heavy metals in fly ash into hardly soluble sulfides by treating them with a sulfurizing agent, so the sulfurizing agent needs to be in close contact with the material to be treated. It is necessary to thoroughly mix the aqueous solution containing the sulfurizing agent and fly ash.

Figures 1 to 3 show several types of fly ash from different sources (each p
A PB elution test was conducted for PB content of 2500 mg/kg), and the median values of each experiment are shown in the figure. Figure 1 shows the percentage of added sulfide based on 100 weight of fly ash.
The horizontal axis is the PB elution B/I! when fly ash is immersed in an aqueous solution 10 times its weight. The unit for the elution amount below c is indicated in accordance with this. This is an example of using fly ash with a water content of 25%, the addition of sulfide was approximately 0.5%, and the amount of PB elution was 3 mg/j? This shows that when the sulfide content is 1% or more, the amount of Pb eluted is practically negligible.

In Figure 2, the vertical axis is the pb elution amount mg/l as before,
On the horizontal axis, the amount of sulfide relative to the fly ash is expressed as twice the molar equivalent of the PB content in the fly ash. As clearly shown in the drawing, when approximately 25 times the molar equivalent of sulfide is added, the elution amount of PB is 3 mg/j! It can be seen that when 50 times the amount or more is added, the amount of pbl eluted becomes negligible. The water content was tested at 25% as in Figure 1.

Figure 3 shows test data on the amount of PB eluted due to the difference in water content of sulfurized fly ash when the added sulfide was 0.5%.The vertical axis is the same as the previous time, and the horizontal The axis shows % moisture content. This clearly shows that the effect of preventing PB elution is insufficient when the water content is low, and this is the basis for supporting the importance of kneading as described at the beginning of this section. There is some variation because the shape and particle size of fly ash and the various forms of heavy metals in fly ash differ depending on the source, but according to the inventor's experiments, when the water content of fly ash is less than 118%, the reaction rate is very poor and the reaction rate is 50%. It became clear that the reaction rate was high, but it was difficult to treat because the mixture turned into a slurry. As the sulfiding agent, sulfides of monovalent alkali metals such as Na and K are preferred because they are water-soluble, but sodium hydrogen sulfide was used in the present invention because of its cost and easy availability. Also, it goes without saying that for fly ash containing far more PB than in this experimental example, it is necessary to increase the amount of sulfurizing agent used. Elution tests were also conducted for heavy metals other than PB, and by adding and mixing about 0.5% sodium hydrogen sulfide, Zn was 1 mg/l, Cu was 0.08
mg/E, T-Cr is 0.01 mg/j! The elution amount was almost negligible. More than PB gold content f
Although 12,500 mg of fly ash has been described, the above values are applicable to PB contents in the range of 600 to 5,000 mg/+r.

(Example) (1) 20 kg of fly ash collected by an electrostatic precipitator in a garbage incinerator (Pb content: 1500 mg/kg)
) into an Eirich counterflow type high-speed mixer, and add 160
g (equivalent to 0.8%) of sodium hydrogen sulfide was added as an aqueous solution, and water was further added by sprinkling to make the water content 30%, and the mixture was sufficiently kneaded with the fly ash. After a predetermined time had elapsed after the completion of the kneading, a part of the fly ash was collected, and 10 times as much water was added to it to detect the amount of heavy metals in the leachate.
2 mg/A, Cu, Cr were tr.

Furthermore, when the same sample was mixed with sodium hydrogen sulfide in an amount of 30 times the molar equivalent of the PB content and mixed with fly ash having a moisture content of 30%, substantially the same results were obtained.

(Effects of the Invention) As detailed above, according to the present invention, heavy metals in the fly ash can be converted into hardly soluble sulfides by simply adding a very small amount of sulfurizing agent and an appropriate amount of water to the garbage incineration fly ash and kneading the mixture. Because it can be converted into fly ash, it can be used safely in landfills and many other places without causing problems due to the elution of heavy metal ions, etc., and is highly effective in preventing pollution and expanding the scope of use of fly ash. There is.

[Brief explanation of the drawing]

Figure 1 is a chart showing the relationship between the addition percentage of sulfide to fly ash and the amount of Pb eluted, and Figure 2 is the value of the amount of sulfide to fly ash expressed as twice the molar equivalent of the Pb content in the fly ash. A chart showing the relationship between PB and the elution amount of PB, Figure 3 shows the added sulfiding agent at 0.5%.
It is a chart showing the relationship between the moisture content of fly ash and the elution amount of PB in the case of . Figure 10 Pavilion Figure 28 Figure 3 #t(S)

Claims (1)

[Claims] Heavy metals in waste incineration fly ash, which is characterized by adding a sulfurizing agent and an appropriate amount of water to the waste incineration fly ash and kneading it to convert the heavy metals contained in the fly ash into hardly soluble sulfides and stabilize them. Stabilization treatment method.