Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
2001-09-17
2002-10-01
Silverman, Stanley S. (Department: 1754)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C588S253000, C588S253000, C588S253000, C405S128800
Reexamination Certificate
active
06459012
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating soil or ash containing organohalogen compounds, and more particularly, to a method for treating an organohalogen compound-containing soil or ash in order to effectively decompose dioxins and dioxin precursors such as aromatic organohalogen compounds or aliphatic organohalogen compounds, e.g., trichloroethylene and dichloromethane, which are contained in the soil or ash.
Exhaust gases, fly ashes and deposited ashes generated from an incinerator upon burning municipal solid wastes and industrial wastes therein, contain dioxins which are aromatic halogen compounds showing an extremely strong toxicity to human bodies, though the contents thereof are very small. The dioxins generally include compounds having such a structure that hydrogen atoms of dibenzo-p-dioxine, dibenzofuran, etc. are substituted with chlorine atoms.
Also, the aliphatic organohalogen compounds such as trichloroethylene and tetrachloroethylene have been extensively used in many applications such as degreasing of metals, dry-cleaning and the like.
The organohalogen compounds have caused significant environmental problems such as air pollution due to discharge thereof into atmospheric air, and contamination of ground water and soils upon disposal thereof, because these compounds are difficult to decompose and show carcinogenesis. In particular, ashes discharged from incinerators or soils contaminated with wastes have a high content of the organohalogen compounds. Therefore, it has been required to decompose these organohalogen compounds and convert these compounds into harmless ones. Although various methods for removing the organohalogen compounds have been conventionally proposed, satisfactory techniques capable of decomposing the organohalogen compounds and converting these compounds into harmless ones in economical and effective manner, have not been established.
Hitherto, various techniques for decomposing organohalogen compounds contained in soils or ashes and converting these compounds into harmless ones have been reported. For example, there are known a method of decomposing poly-halogenated aromatic compounds having at least five carbon atoms by heating at a temperature of 200 to 550° C. in the presence of a catalyst such as iron oxide (Japanese Patent Publication (KOKOKU) No. 6-38863(1994)); a method of removing halogenated aromatic compounds or the like from an exhaust gas or reducing amounts thereof by heat-treating at a temperature of 300 to 700° C. in the presence of a catalyst containing iron oxide (Japanese Patent Application Laid-Open (KOAKI) No. 2-280816(1990)); a method of introducing an inhibitor for preventing the generation of dioxins composed of an amine-carrying activated carbon, into an exhaust gas passing through flues of an incinerator (Japanese Patent Application Laid-Open (KOAKI) No. 11-9960(1999)); a method of mixing ashes to be treated, and a dechlorinating agent, and then heat-treating the resultant mixture (Japanese Patent Application Laid-Open (KOAKI) No. 11-19616(1999)); a method of decomposing organohalogen compounds in the presence of oxygen using a solid catalyst containing iron oxide, etc. and/or titanium dioxide as base components (Japanese Patent Application Laid-Open (KOAKI) Nos. 11-188235(1999) and 11-188236(1999)); a method of adding phosphorous acids, hypophosphorous acids with an aluminum compound, and/or a titanium compound to solid wastes and then heat-treating the resultant mixture (Japanese Patent Application Laid-Open (KOAKI) No. 11-290824(1999)); or the like.
In addition, there are also known an iron compound catalyst having a specific catalytic activity, and a method of spraying the iron compound catalyst into a combustion chamber of an incinerator in order to prevent the generation of dioxins (Japanese Patent Application Laid-Open (KOAKI) No. 11-267507(1999)).
However, although it has been presently required to provide an process for decomposing the organohalogen compounds contained in soils or ashes and converting these compounds into harmless ones, the methods described in the above publications are still unsatisfactory.
Namely, in the method described in Japanese Patent Publication (KOKOKU) No. 6-38863(1994), poly-halogenated compounds which are contained in fly ashes generated in an incinerator or solid wastes are decomposed under an oxygen-lack atmosphere or an inert gas atmosphere in a non-pass-through-type or closed-type apparatus using fly ashes, metals, metal oxides containing iron oxide, carbonates, silicates and the like as a catalyst. However, this method must be performed under the specific conditions, i.e., under the closed system or the inert gas atmosphere, thereby requiring large-scale apparatuses with high air-tightness as well as high costs for installation and maintenance thereof. Therefore, the above method is unsatisfactory from industrial viewpoints.
In the method described in Japanese Patent Application Laid-Open (KOAKI) No. 11-19616(1999), after incineration ashes, fly ashes or the like are mixed with a dechlorinating agent composed of alkali substances, the resultant mixture is heat-treated. In this method, it is required to contact chlorine-containing gases generated by heating the wastes to be treated, with the alkali substances. Thus, the wastes to be treated must be heated to an elevated temperature in order to generate the chlorine-containing gases. Namely, the method is not directly concerned with such techniques for decomposing the organohalogen compounds and converting these compounds into harmless ones. Therefore, the above method is also unsatisfactory to convert dioxins into harmless compounds.
In the method described in Japanese Patent Application Laid-Open (KOAKI) No. 11-9960(1999), the amine-carrying activated carbon is introduced into exhaust gases containing dioxins in order to adsorb the dioxins in the activated carbon by high adsorptivity of the activated carbon, and then react the dioxins with the amine compound for decomposition of the dioxins. The amine-carrying activated carbon exhibits a high dioxin-adsorptivity, but is insufficient in dioxin-decomposition activity. Further, the activated carbon cannot sufficiently prevent the generation of dioxins. Also, the activated carbon tends to be ignitable and flammable when heated to an elevated temperature. Therefore, the above method is undesirable in view of safety.
In the method described in Japanese Patent Application Laid-Open (KOAKI) Nos. 11-188235(1999) and 11-188236(1999), organohalogen compounds contained in gases are decomposed in the presence of oxygen using a solid catalyst containing iron oxide, etc. and/or titanium dioxide as base components. Thus, the organohalogen compounds treated by the method are only those contained in gases, the above method is unsatisfactory for decomposing organohalogen compounds contained in solids.
In the method described in Japanese Patent Application Laid-Open (KOAKI) No. 11-290824(1999), there is used a treating agent containing phosphorous acids and hypophosphorous acids. As shown in Comparative Examples below, the treating agent is poor in dioxin-decomposition percentage. Therefore, the above method is also unsatisfactory for decomposing dioxins.
Further, the catalyst described in Japanese Patent Application Laid-Open (KOAKI) No. 11-267507(1999), is effective to reduce the amount of dioxins contained in soils or ashes. However, the activity of the catalyst is still unsatisfactory as shown in Comparative Examples below.
As a result of the present inventors' earnest studies for solving the above problems, it has been found that by mixing organohalogen compound-containing soil or ash with a specific organohalogen compound-decomposition catalyst and then heat-treating the resultant mixture at a temperature of 150 to 600° C., it is possible to effectively decompose dioxins or dioxin precursors contained in the soil or ash. The present invention has been attained on the basis of this finding.
SUMMARY OF THE INVENTION
It is an object of the pr
Fujii Yasuhiko
Hakata Toshiyuki
Hatakeyama Satoshi
Imai Tomoyuki
Matsui Toshiki
Nave Eileen E.
Nixon & Vanderhye P.C.
Silverman Stanley S.
Toda Kogyo Corporation
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