JPH0577477B2 - - Google Patents

Description

[Detailed description of the invention] "Objective of the invention" (Industrial application field) Stabilization that allows heavy metals contained in waste incineration fly ash to be efficiently converted into compounds that are difficult to elute under easy-to-handle conditions. This relates to a processing method.

(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 its disposal has become a major problem in urban environmental administration. In other words, fly ash generally contains heavy metals that are harmful to the human body.
Since it exists in the form of stable oxides and other soluble salts such as chlorides and sulfates, it cannot be easily disposed of in landfills, and even if it is solidified with cement. Also, lead etc. may leach out and cause problems.

However, the conventional method for stabilizing heavy metals is as follows: Japanese Patent Application Laid-Open No. 53-12772: Add an acidic solution to fly ash to dissolve heavy metals, filter it, and add iron salt to the solution to generate ferrite. A method for separating heavy metals by causing a reaction and 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 dissolve heavy metals into water. A method of precipitating oxides, filtering this slurry, and sintering and solidifying the residue, Japanese Patent Publication No. 60-52876: After adding acid to fly ash to dissolve heavy metals, it is filtered, and this solution is treated with alkali or sulfide. A method of precipitating heavy metals, filtering them, and melting and solidifying the residue, JP-A-59-73091: Adding Na ₂ to incinerator dust ash, etc.
This involves adding and kneading an alkaline soluble sulfide with a reducing function selected from Sl, K ₂ Sm, CaSn, etc. In each test example, 0.05 to 10 ml of ash was added to 100 g of ash. No.: There is a method of adding and mixing 8 to 15 parts by weight of a treatment agent such as sodium sulfide to 100 parts by weight of collected dust or incineration ash containing harmful substances such as heavy metals. However, the methods described above require complicated treatment steps such as filtration or sintering and solidification, and have the disadvantage that the treatment cost is very high. There were concerns that this would cause secondary pollution, as large amounts of salt would need to be discharged.

In addition, the above-mentioned methods all limit the water content to about 10 to 13% by adding a treatment agent,
The reaction rate is insufficient and therefore there is a great risk of secondary pollution. Moreover, in the case of garbage incineration fly ash, the fly ash scatters significantly during mixing and cargo handling.

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

"Structure of the invention" (Means for solving the problem) A sulfurizing agent and water are added to garbage incineration fly ash, and the moisture content is 18~18.
A method for stabilizing heavy metals in garbage incineration fly ash, which comprises mixing the fly ash at a concentration of 30% to stabilize the heavy metals contained in the fly ash by converting them into hardly soluble sulfides.

(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 Pb elution tests performed on several types of fly ash from different sources (each PH content 2500 mg/Kg) using sodium bisulfide as a sulfiding agent, and the median values of each experiment are combined. This is illustrated in the figure. In Figure 1, the horizontal axis shows the percentage of added sulfiding agent based on the weight of fly ash (100%), and the vertical axis shows the percentage of fly ash relative to its weight.
Pb elution mg/when immersed in 10x aqueous solution
(Hereinafter, the units of elution amount will be in accordance with this).
This is an example of using fly ash with a water content of 25%, and when the sulfurizing agent was added at approximately 0.5%, the amount of Pb eluted was approximately 3 mg/kg, and if the sulfurizing agent was 1% or more, Pb was practically eluted.
The amount is shown to be negligible.

In Figure 2, the vertical axis is the amount of Pb elution mg/mg as in the previous figure.
On the horizontal axis, the amount of sulfurizing agent relative to fly ash is expressed as twice the molar equivalent of the Pb content in fly ash. As clearly shown in the drawing, when approximately 25 times the molar equivalent of the sulfurizing agent is added, the amount of Pb eluted is approximately 3 mg/, and when more than 50 times the amount is added, the amount of Pb eluted becomes negligible. I know that there is. Water content is the first
The test was conducted at 25% as in the case shown in the figure.

Figure 3 shows test data on the amount of Pb eluted due to the difference in moisture content of sulfurized fly ash when the added sulfiding agent was 0.5%.The vertical axis is the same as in the previous figure, and the horizontal axis is the same as the previous figure. % moisture content is indicated. 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. Although there is some variation as the shape, particle size, and various forms of heavy metals in fly ash differ depending on the source, the inventor's experiments showed that when the moisture content of fly ash was less than 18%, the reaction rate was very poor. On the other hand, if it exceeds 30%, it becomes muddy and the reaction rate is high, but it becomes clear that it is difficult to treat. Therefore, as shown in Figure 3, the water content is 25%.
By setting the Pb elution amount to 3 mg/ and setting the water content to 30% as the upper limit, it is possible to achieve a suitable treatment with a Pb elution amount of about 1 mg/. In particular, when the moisture content exceeds 18% due to the relationship with fly ash minute particles, the mixed fly ash forms pellet-like lumps.
After proper mixing, fly ash will not be scattered during further mixing operations or cargo handling such as shipping. In addition, if the water content exceeds 30%, the mixture becomes muddy and adheres to the car body or bucket when being loaded onto a transport vehicle using a crane, making it difficult to unload the mixture smoothly. However, by setting it to 18 to 30%, all of these disadvantages can be appropriately eliminated and processing with excellent handling properties can be carried out. The above-mentioned sulfiding agent is preferably a water-soluble sulfide, and a chelating agent for a liquid containing S and a sulfide of a monovalent alkali metal such as Na or K are suitable. In the present invention, sodium hydrosulfide was used. Furthermore, 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. In addition, elution tests were also conducted for heavy metals other than Pb, but by adding and mixing approximately 0.5% sodium hydrogen sulfide, Zn was 1 mg/, Cu
The elution amounts were approximately 0.08 mg/for T-Cr and 0.01 mg/for T-Cr, which were almost negligible. Pb content more than 2500
mg of fly ash, but each of the above values is Pb
It can be applied to products with a content in the range of 600 to 5000 mg/Kg.

(Example) (1) 20 kg of fly ash (Pb content 1500 mg/Kg) collected by the electrostatic precipitator of a garbage incinerator was put into an Eirich backflow type high-speed mixer, and 160 g (0.8
% equivalent) of sodium hydrogen sulfide as an aqueous solution,
Further, water was added by sprinkling to bring the water content to 30%, and the fly ash was sufficiently kneaded with the fly ash.The fly ash formed a coagulated state due to the moisture, and was obtained in the form of particles of several millimeters in size. After a predetermined time had elapsed after the completion of kneading, a portion 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.
Zn0.02mg/, Cu, and Cr were tr.

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

(Effects of the Invention) As detailed above, according to the present invention, heavy metals in the fly ash can be made sticky by simply adding a very small amount of sulfurizing agent and a specific amount of water to garbage incineration fly ash and kneading it. Because it can be converted into a poorly soluble sulfide under easy processing conditions without causing significant adhesion to work equipment, it can be used in landfills and in many other places.
It is highly effective in preventing pollution and expanding the scope of use of fly ash, as it does not cause troubles due to the elution of heavy metal ions, etc., and it can be used easily and with peace of mind.

[Brief explanation of drawings]

Figure 1 is a chart showing the relationship between the addition percentage of sulfurizing agent to fly ash and the amount of Pb eluted, and Figure 2 is the value of the amount of sulfurizing agent to fly ash expressed as twice the molar equivalent of the Pb content in fly ash. A chart showing the relationship between Pb and the elution amount of Pb,
FIG. 3 is a chart showing the relationship between the moisture content of fly ash and the amount of Pb eluted when the added sulfiding agent is 0.5%.

Claims (1)

[Claims] 1 Add a sulfiding agent and water to garbage incineration fly ash to obtain a water content of 18
A method for stabilizing heavy metals in garbage incineration fly ash, which comprises mixing the fly ash with a concentration of up to 30% to convert and stabilize the heavy metals contained in the fly ash into hardly soluble sulfides.