Furnaces – Process – Incinerating refuse
Patent
1991-01-28
1992-12-08
Favors, Edward G.
Furnaces
Process
Incinerating refuse
110236, 110238, F23G 704
Patent
active
051688204
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the production of clinkers from sludges containing heavy metals, especially electroplating sludges, river and/or harbor sludges, in which the electroplating are mixed with clay, especially brickyard clay, and optionally lean materials and fluxing materials and then are burned to clinkers especially at temperatures between 750.degree. and 1150.degree. C.
A process of the initially mentioned type can be gathered, for example, from AT-PS 387 766. The previously known process was developed for the disposal of sludges containing heavy metals, as they occur especially in industrial pickling units or electroplating plants and by the binding of the heavy metal compounds or heavy metals in a clinker a product was provided in which the sludges containing heavy metals, too are enclosed in a largely vitrified mass, by which the danger of an elution of water-soluble heavy metal salts was substantially reduced. At the same time, with the clinkers a product was provided which is marked by characteristic dark shades and could be used in the construction industry. The previously known process in this case was performed so that the period of burning of the mixture of clay and sludges containing heavy metals was selected as a function of the desired lower residual porosity, and a residual porosity clearly below 6% was aimed at. The burnt products in this case are largely neutral so that even in acid rain only slight leaching of the heavy metal salts could be observed. At this point, clinkers are substantially distinguished from construction materials whose stability is achieved by hydraulic binding. Gypsum or concrete are therefore unsuitable for safely enclosing sludges containing heavy metals from washing out, since unlike clinkers they are not resistant to chemical attacks, e.g. chloride, sulfate, acid rain, etc. and large amounts of heavy metal salts can be washed out.
For the clinker production pulverized grog or the like is mostly used as lean material and the bricks can be molded in vacuum extruders.
To improve the elution behavior it was already proposed in AT-PS 387 766 to add neutral or acid additives, such as silicon dioxide or an active siliceous earth product, to the brickyard clay. Burning to clinkers leads to a conversion of the heavy metal compounds to oxides of low solubility and the additives proposed at that time were supposed to cause an acceleration of the vitrification. Besides this action accelerating the vitrification, a cation exchange action was already ascribed to such siliceous earth products, since such products are effective as Lewis acids. The additives act, moreover, in such a way that the porosity is reduced and thus washing out of metal was supposed to be made even more difficult.
Depending on the origin of the sludges, it is generally necessary to neutralize acid waters, and heavy metals form precipitates as hydroxides. But the formed hydroxides partially exhibit amphoteric properties and have their solubility maxima at different pH's. This means that at least a part of the heavy metals is present in soluble form. Such water-soluble compounds can be bound only inadequately in clinkers and in the drying process come to the surface of the clinkers with the water. Thus an unwanted concentration of such compounds occurs in the near-surface layers, which subsequently, even if these compounds near the surface are converted to the greatest extent possible into insoluble oxides during burning, increased elution values result for these heavy metals, especially under conditions of an acid rain.
The invention aims at providing a mixture for the production of clinkers, in which, when drying, the danger of a migration of water-soluble heavy metal compounds to the near-surface areas is very largely prevented, and which altogether guarantees a more homogeneous concentration distribution of the heavy metal compounds in the interior of the clinkers, so that the elution properties, especially in conditions of an acid rain, are further improved. To achieve this object th
REFERENCES:
patent: 4583470 (1986-04-01), Hirose
patent: 5037561 (1991-08-01), Copeland
Chemistry & Industry, No. 7, Apr. 2, 1984, (Letchworth, Herts, GB), J. Dwyer et al.: "Zeolites for Industry", pp. 237-245.
Birkner Friedrich
Schwarz Wolfgang
Favors Edward G.
Magindag Steirische Magnesit-Industrie Aktiengesellschaft
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