Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
2000-02-02
2003-10-28
Shackelford, Heather (Department: 3673)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C588S253000, C588S252000
Reexamination Certificate
active
06638204
ABSTRACT:
TECHNICAL FIELD
The present invention relates to passivation of the heavy metals in heavy metal-containing wastes. More precisely, it relates to methods of treating heavy metal-containing wastes suitable to passivating the heavy metals such as lead, cadmium, chromium and others in the wastes. The invention also relates to sealants suitable to the treatment. It further relates to solidified substances with high mechanical strength formed in the treatment.
TECHNICAL FIELD
Urban and industrial garbage and wastes are greatly increasing these days, and heavy metals often exist in the incinerated ash or fly ash discharged through incineration of such wastes. For protecting the environment, therefore, desired are some safe measures to make the incinerated ash or fly ash harmless.
One conventional method which has heretofore been proposed for that purpose comprises solidifying heavy metal-containing wastes with cement to thereby passivate the heavy metals in the solidified wastes. According to the method, however, it is difficult to completely passivate the heavy metals so as not to make them released at all from the solidified wastes. In addition, another problem with the method is that curing cement takes a lot of time.
Another method has been proposed, which comprises releasing the heavy metals from wastes by the use of mineral acids. However, the method is also problematic in that the metal-releasing acid treatment requires complicated operations and that an additional step of separately solidifying the wastes is needed.
On the other hand, disclosed is a method comprising adding a water-soluble sulfide, such as sodium sulfide, calcium sulfide or the like, to incinerator ashes and others discharged from usual incinerators, and kneading them to thereby passivate the heavy metals, such as lead, cadmium and others in the incinerator ashes and make them harmless, for example, in Japanese Patent Laid-Open Nos. 39262/1978, 1830/1980, 73091/1984, 111990/1988 and 24355/1997. In those, the method disclosed is to passivate the heavy metals in incinerator ashes into inert sulfides such as lead sulfide and others, thereby making them harmless. As a rule, however, the solubility of heavy metal sulfides in water is extremely low. Therefore, the particles of the heavy metal sulfides formed and deposited in the method are extremely fine, having a particle size of around 0.01 microns or so, and, in addition, many of them have relatively high dispersibility in water. For these reasons, the method disclosed is problematic in that the heavy metal sulfide particles formed therein pass through a paper filter having a mean pore size of 1 micron in the test stipulated in Notification No. 13 of the Director General of the Environment Agency of Japan. Japanese Patent Laid-Open No. 203981/1990 discloses a method of using a polymer substance with an organic carboxylic acid for solving the problem. However, the method is still problematic, as it is not economical.
DISCLOSURE OF THE INVENTION
Taking the above into consideration, we, the inventors have made the present invention, of which one object is to provide methods of treating heavy metal-containing wastes capable of efficiently and stably passivating the heavy metals in the wastes to thereby prevent the thus-passivated heavy metals from being released from the wastes.
Another object of the invention is to provide sealants and sealant promoters suitable to efficiently and stably passivating the heavy metals in heavy metal-containing wastes, etc.
Still another object of the invention is to provide compounds or compositions suitable to efficiently and stably passivating the heavy metals in heavy metal-containing wastes, etc. The compounds or compositions may be used as the sealant for passivating the heavy metals in heavy metal-containing wastes, etc.
Still another object of the invention is to provide solidified substances with high mechanical strength formed in the treating methods.
Specifically, the invention is summarized as follows:
(1) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes, (B) an alkali metal compound or an alkaline earth metal compound and (C) sulfur in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
(2) The method of above (1) for treating heavy metal-containing wastes, wherein the alkali metal compound or the alkaline earth metal compound (B) is an alkali metal or alkaline earth metal hydroxide or oxide.
(3) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes and (D) a sulfide in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
(4) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes, (B) an alkali metal compound or an alkaline earth metal compound, (C) sulfur and (E) a salt of a metal of which the standard electrode potential is higher than that of the cation of the component (B), in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
(5) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes, (B) an alkali metal compound or an alkaline earth metal compound and (C) sulfur in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture, and in which the component (A) and the component (C) are melted and kneaded before the component (B) is added thereto.
(6) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes, (D) a sulfide and (F) a salt of a metal of which the standard electrode potential is higher than that of the cation of the component (D), in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
(7) The method of any one of above (4) or (6) for treating heavy metal-containing wastes, wherein the sulfide (D) is an alkali metal or alkaline earth metal sulfide.
(8) The method of any one of above (1) to (7) for treating heavy metal-containing wastes, wherein the non-aqueous is at least one selected from sulfur, asphalt, thermoplastic resins and thermosetting resins.
(9) The method of above (1) for treating heavy metal-containing wastes, wherein the component (B) and the component (C) are individually in the form of master batch pellets with the non-aqueous medium (except sulfur).
(10) A solidified substance with high mechanical strength, which is formed in any one method of above (1) to (9).
(11) A sealant for heavy metals, which comprises (B) an alkali metal compound or an alkaline earth metal compound and (C) sulfur.
(12) A sealant for heavy metals, which comprises (B) an alkali metal compound or an alkaline earth metal compound, (C) sulfur, and a non-aqueous medium.
(13) The sealant for heavy metals of above (12), wherein the non-aqueous medium is at least one selected from sulfur, asphalt, thermoplastic resins and thermosetting resins.
(14) The sealant for heavy metals of any one of above (11) to (13), wherein the ratio of the alkali metal compound or the alkaline earth metal compound (B) to the sulfur (C), (B)/(C) by mol, falls between 0.2 and 3.
(15) The sealant for heavy metals of any one of above (11) to (14), wherein the alkali metal compound or the alkaline earth metal compound (B) is an alkali metal or alkaline earth metal hydroxide or oxide.
(16) An alkali metal or alkaline earth metal sulfide as obtained by reacting (B) an alkali metal compound or an alkaline earth metal compound with (C) sulfur with stirring at 50 to 170° C. for 1 to 20 minutes.
(17) An alkali metal or alkaline earth metal sulfide of above (16), for which the ratio of the alkali metal compound or the alkaline earth metal compound (B) to the sulfur (C), (B)/(C) by mol, falls between 0.2 and 3.
(18) A sealant for heavy metals, which comprises the alkali metal or al
Akagawa Toshiyuki
Hachiya Satoshi
Mizutani Makoto
Idemitsu Kosan Co. Ltd.
Kreck John
Shackelford Heather
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