Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1997-08-05
2000-05-30
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75623, 75628, 75638, 75690, 75703, 75958, 423594, C22B 700
Patent
active
060686774
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for processing waste or waste fractions, such as, e.g., household refuse, car shredder light fractions or the like, by subjecting the charging material to pyrolysis, gasification and/or combustion.
2. Description of the Related Art
Known methods for such waste processing are aimed at ensuring slagging to as large an extent as possible, whereupon higher-grade end products are to be obtained by a suitable aftertreatment of the slag. Thus, the aim of known procedures was to initally ensure complete slagging to as large an extent as possible and completely oxidize any combustible components, whereupon portions or alloys capable of being metallized by concerted reduction steps were again separated from the slag.
Especially with residues strongly loaded with heavy metals and, in particular, chromium-containing residues such a slag melt, complete oxidation of the starting materials is extremely agressive. Also, it has been proved that the separation of extremely troublesome components, such as chromium, in classical process control is feasible only at the end of the process and not to the extent desired and that all of the preceding fractions remain more or less strongly contaminated, for instance, with chromium.
SUMMARY OF THE INVENTION
The invention aims at providing a method of processing waste in which undesired metals can more readily be separated and by which purer products can be made available for further processing. The invention, in particular, aims at producing synthetic blast furnace slag and at separating marketable metal compounds and metal alloys. To solve this object, the invention essentially resides in that the residues from pyrolysis, gasification and/or combustion are heated under reducing conditions and that the reduced metallic components are subjected to stepwise oxidation, wherein in a first oxidation stage sufficient oxygen is made available to ensure the quantitative reaction to chromic iron. By the fact that the residues mentioned above are no longer subjected to complete oxidation as opposed to the known mode of procedure, but, by contrast, are melted under reducing conditions, a slag is immediately formed in which the portion of metal oxides is substantially reduced. Above all, it can be ensured that the slag drawn off the reducingly run shaft furnace offers a substantially better purity, since the slag is not inadmissibly contaminated with heavy metals and/or chromium. Heavy-metal chlorides will volatilize by the reducing mode of procedure taking place within the shaft furnace and may be recovered in the form of filter dusts. Such filter dusts as, for example, CuCl, ZnCl.sub.2 and PbCl.sub.2 subsequently may be washed basic and added to the consecutively arranged oxidation converter prior to refining, wherein the heavy-metal oxides formed are reduced and zinc, lead, cadmium or mercury may, for instance, be recovered from the gaseous phase. With that mode of procedure, copper, nickel, tin and antimony enter into the metal bath; chromium is quantitatively separable in a particularly simple manner already by a first oxidation. That quantitative separation of chromium in a first oxidation stage following upon the reducing melting procedure will directly result in substantially purer further products, which, in the following, may be processed to usable metals or metal alloys. The early elimination of chromium consequently also reduces the risk of the converter lining being destroyed prematurely and at the same time renders feasible the obtainment of an intermediate product to be readily utilized later on for recovering chromium.
Advantageously, the chromium-containing spinel floating on the surface is drawn off and reduced to a ferro-chromium-carbure alloy. As an alternative, oxidation to chromium oxide might, of course, also take place. At refining temperatures of above 1350.degree. C. the chromium oxide formed, which has a melting point of 2435.degree. C., would likewise be separated and likewise
REFERENCES:
patent: 5302184 (1994-04-01), Batterham et al.
Patent Abstracts of Japan, vol. 96, No. 3, Mar. 29, 1996 & JP 07 30031 A; Nov. 14, 1995.
"Holderbank" Financiere Glarus AG
Andrews Melvyn
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