Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Patent
1995-07-14
1997-05-06
Suchfield, George A.
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
405128, 588252, B09B 300
Patent
active
056265522
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a waste treatment method capable of effectively stabilizing wastes containing hazardous metals, and more particularly, to a waste treatment method capable of effectively stabilizing fly ash (resulting from waste incineration) containing lead which is subject to leaching owing to calcium compounds (such as calcium hydroxide, calcium oxide, and calcium chloride) contained therein.
BACKGROUND ART
The prevailing method for treatment of industrial waste containing hazardous metals consists of mixing it with cement and kneading the resulting mixture with water, followed by curing and solidification, so that hazardous metals are stabilized to prevent their leaching. However, simply solidifying industrial waste with cement involves several problems associated with secondary pollution, unless its application is limited. For example, when treatment with cement according to the prior art technology is applied to fly ash collected by an electrostatic precipitator or bag filter at the time of waste incineration, it cannot completely prevent the leaching of lead contained therein in high concentrations. To make matters worse, lead in the ash of waste is more liable to leaching in the alkaline environment, as known well. Since the incinerator for municipal solid waste is fed with slaked lime to suppress the evolution of hydrochloric acid, it gives rise to fly ash containing calcium compounds, such as slaked lime (or calcium hydroxide), calcium chloride (as a reaction product of slaked lime and hydrochloric acid), and calcium oxide (resulting from the heating of slaked lime). Fly ash collected by an electrostatic precipitator or bag filter under such operating conditions contains a large amount of leachable lead. With the prior art technology, it is impossible to completely prevent the leaching of lead. Therefore, at the present time, it is common practice to dump such fly ash without hazardous metals being fully stabilized, and such dumping is presenting problems associated with secondary pollution.
It has become apparent inside and outside the country that it is difficult to stabilize industrial waste containing hazardous metals so as to prevent their leaching by simple solidification with cement. This has stimulated the development of a new waste treatment method which permits safe dumping on land and at sea without the possibility of heavy metals leaching out to cause secondary pollution.
The present invention was completed in view of the current state of waste treatment. Accordingly, it is an object of the present invention to provide a waste treatment method capable of certainly solidifying and sealing industrial waste containing hazardous metals, thereby stabilizing it such that hazardous metals will not leach out after dumping.
DISCLOSURE OF THE INVENTION
The gist of the present invention resides in a waste treatment method which comprises mixing waste containing calcium compounds (such as calcium hydroxide, calcium oxide, and calcium chloride) with a treating agent composed mainly of water glass and optional water such that the total amount of water is 25-75 parts by weight for 100 parts by weight of waste, and kneading the resulting mixture.
The present invention may employ water glass of general-purpose type. Water glass is represented by the formula M.sub.2 O.nSiO.sub.2 (where M denotes a cation). Examples of the cation (as an alkaline component) include sodium and potassium. Water glass containing sodium as the cation (which is sodium silicate) is preferable from the standpoint of availability and price. In addition, this water glass should preferably contain M.sub.2 O and SiO.sub.2 in a ratio of from 0.5 to 4 (which is denoted by n) for the same reason as above. The water glass used in the present invention may contain inevitable impurities, such as iron, which will present no problems. The water glass may be available in the form of either solid or liquid.
According to the present invention, the amount of water glass to be added varies depending on the
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patent: 4505851 (1985-03-01), Funabashi et al.
patent: 4600514 (1986-07-01), Conner
patent: 4687373 (1987-08-01), Falk et al.
patent: 5457273 (1995-10-01), Glover et al.
Kuromatsu Hidekazu
Nomura Takuji
Uekita Masakazu
Kanegafuchi Kagaku Kogyo & Kabushiki Kaisha
Suchfield George A.
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