JP3986055B2 - Purification method for contaminated soil - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying contaminated soil or the like, which detoxifies organic chlorine compounds such as dioxins and heavy metals by mixing one or both of a silanol salt and siloxane with the contaminated soil and heat-treating it.
[0002]
[Prior art]
Bioremediation using microorganisms has been proposed as a method for repairing contaminated soil with harmful organic compounds, but there are difficulties in terms of the efficiency of decomposition and removal of pollutants and treatment costs.
It has been pointed out as a problem that microorganisms can adversely affect the ecosystem in the soil, and degradation by microorganisms takes time, so that rapid treatment cannot be expected.
Microorganisms can change organic compounds to other types of substances, but cannot detoxify heavy metals in soil, and bioremediation cannot repair heavy metal contamination.
In recent years, not only organochlorine compounds but also complex contamination due to heavy metals has been recognized in the soil of sites such as factories and the like, and a technique for easily and quickly treating these has been strongly demanded.
However, according to such a conventional technique, it is not only difficult to decompose and remove harmful organic compounds, but it is impossible to detoxify organochlorine compounds and heavy metals simultaneously.
[0003]
[Problems to be solved by the invention]
In view of the problems of the prior art, the present invention can reliably detoxify not only organochlorine compounds such as dioxins but also complex contaminated soil with heavy metals by a simple method, and at the same time, it enables purification and repair. The purpose is to provide the technology.
[0004]
[Means for Solving the Problems]
In order to achieve such an object, the gist of the present invention is to add silanol salt, siloxane, or both to complex contaminated soil containing both harmful organochlorine compounds and harmful heavy metals, and heat to 380 ° C. or higher. The heat treatment is preferably performed at 580 ° C. or more, and both are made harmless at the same time .
The organic chlorine compound may be dioxins.
Here, the silanol salt is a compound containing mono-, di-, or tri-silanol and a metal salt thereof, and is at least partially silicon oxide structure (Si-O) by thermal decomposition at 380 ° C or higher. The thing that becomes.
Siloxane refers to a compound containing at least a substance having a Si—O—Si bond in a compound and having a silicon oxide structure at least partially by thermal decomposition at 380 ° C. or higher.
Note that a fluorine element may be contained in the silanol salt or siloxane.
Dioxins refer to dioxin that is a chlorine-substituted product of dibenzopararadixin (PCDD), chlorodibenzofuran that is a chlorine-substituted product of dibenzofuran (PCDF), and PCB (polychlorobiphenyl).
[0007]
In the present invention, dioxins, dichloromethane, carbon tetrachloride, 1.2-dichloroethane, 1.1-dichloroethylene, cis-1.2-dichloroethylene, 1.1.1-trichloroethane, 1.1.2 -By adding silanol salt and siloxane to contaminated soil containing harmful organic chlorine compounds such as trichloroethane, trichlorethylene, tetrachloroethylene and 1.3-dichloropropene, and heating them to 380 ° C or higher, preferably 580 ° C or higher. Organochlorine compounds are volatilized and decomposed, and these decomposition products are incorporated and fixed in a framework structure of silicon oxide formed by thermal decomposition of silanol salt and siloxane, and rendered harmless.
A chlorine compound that is a decomposition product of dioxins and also serves as a precursor at the time of production can be similarly taken in and fixed.
That is, it is possible to fix the decomposition product of dioxins and simultaneously suppress resynthesis from the decomposition product.
[0008]
In addition, silanol salt and siloxane are added to contaminated soil containing harmful heavy metals such as cadmium, lead, chromium, arsenic, mercury, copper, selenium, and heated to 380 ° C or higher, preferably 580 ° C or higher. Heavy metal is incorporated into the framework structure of silanol salt and siloxane is generated by thermal decomposition, becomes solid solution and is fixed in the soil, and its elution into aqueous solution, that is, groundwater system is suppressed and harmless It becomes.
[0009]
Furthermore, by adding silanol salt and siloxane to soil contaminated with organic chlorine compounds and heavy metals such as dioxins and heating them to 380 ° C or higher, preferably 580 ° C or higher, Both the organochlorine compound and heavy metal to be detoxified can be treated simultaneously.
[0010]
Soil is generally composed of silicon oxide, aluminum oxide, and salts thereof, but silanol salt and siloxane are thermally decomposed into a silicon oxide-based structure at about 380 ° C. depending on the type, and at about 580 ° C. or higher. Many siloxanes have a silicon oxide structure, which results in a silicon oxide-based material that is similar to the soil, thus creating no harmful chemicals and polluting the soil without impacting the environment. It can be purified and repaired.
Since silanol salt and siloxane show alkalinity, they have the effect of soil improvement as well as detoxification treatment of organic chlorine compounds and heavy metals.
Although generation of fly ash is generally a concern during heat treatment, fly ash can be incorporated into the silicon oxide skeleton by mixing and heating a silanol salt and siloxane in the treatment process according to the present invention. There is also an effect of reducing the amount of generation.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Sampling the soil of Nose-cho, Toyono-gun, Osaka, contaminated with dioxins discharged from a garbage incinerator, mixing about 10% by mass of pre-treatment, silanol salt and siloxane at about 900 ° C, Fig. 1 shows the dioxin content after heat treatment for about 1 hour (according to the soil interim survey manual for dioxins).
Dioxins contained in 3100 pg-TEQ per gram of dry weight before treatment were reduced to 0.61 pg-TEQ, approximately 1/5000, by heat treatment with addition of siloxane and silanol salt.
Before processing, it exceeded 3000 pg-TEQ / g, which is the standard of the Dioxin Countermeasures Law, but after processing, it was less than 40 pg-TEQ / g, the environmental standard of German farmland, which is considered to be the most severe .
[0012]
Figure 2 shows the results of heavy metal elution test after sampling the soil at the rubbing site of the waste incinerator, mixing the pre-treatment soil with about 5% by mass of silanol salt and siloxane, and heating at about 900 ° C for about 30 minutes. (According to Environmental Agency Notification No. 13).
Before the treatment, the lead elution test result exceeded the environmental standard related to soil contamination, but after the treatment, it was below the detection limit (indicated as ND).
Other cadmium and mercury also resulted in a decrease in the elution concentration after treatment than before treatment.
It was confirmed that elution of heavy metals was suppressed by mixing and heat-treating siloxane and silanol salts.
[0013]
FIG. 3 shows an example of a purification process procedure for contaminated soil and the like according to the present invention.
Collect contaminated soil, mix siloxane and silanol salt, heat-treat in a baking furnace, and return the treated soil to its original land.
These treatment processes can also be performed by bringing a firing furnace to the site.
The firing furnace may be a batch type or a kiln furnace.
[0014]
【The invention's effect】
According to the present invention, soil contaminated with harmful organic chlorine compounds such as dioxins and heavy metals can be rendered harmless by adding a silanol salt or siloxane and heat-treating it.
In particular, there is an excellent effect of being able to treat harmful organic chlorine compounds and heavy metal contamination at the same time.
In addition, the method of heat treatment with addition of siloxane and silanol salts has less impact on the soil environment such as ecosystems than other methods of purification using microorganisms, and there is no adverse effect associated with the purification treatment. It has excellent characteristics.
[Brief description of the drawings]
FIG. 1 shows dioxin content measurement results before and after detoxification treatment according to the present invention.
FIG. 2 shows the results of heavy metal dissolution tests before and after detoxification treatment according to the present invention.
FIG. 3 shows an example of a procedure for purification treatment of contaminated soil or the like in the present invention.

Claims (1)

Mix toxic organochlorine compounds and toxic heavy metals present in the soil with silanol salts, siloxanes, or both in the soil at 5% by mass or more with respect to the amount of the soil to 380 ° C or higher. A method for purifying contaminated soil , comprising heating, simultaneously detoxifying, fixing to a silicon oxide-based substance, and repairing the contaminated soil .

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