Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1992-08-13
1994-11-15
Andrews, Melvyn J.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 1063, 75416, 75430, 75961, 423107, C22B 702
Patent
active
053644417
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the treatment of wastes and is more particularly concerned with treatments which are environmentally beneficial and efficient.
In this specification, some embodiments of the invention will be described in terms of a process using fine particulate wastes containing iron values and which are generally referred to as steelworks dusts. In modern steelmaking such ferruginous dusts are produced particularly during oxygen steelmaking and electric steelmaking, the dust frequently containing significant zinc values. In some steel making plants, a wet process is used for removing the waste and the steelworks dusts are in the form of a sludge, but in this specification the term "steelworks dusts" will be used to cover the fine wastes from steelworks whether in dust form or sludge form. However, it is to be understood that the invention is not necessarily limited just to the processing of such steelworks dusts and analogous applications may exist.
Generally steelworks are located in areas having substantial populations in the vicinity and accordingly having a major problem in dealing with sewage sludges, the disposal of which is often environmentally harmful. Sewage sludges may contain pathogens as well as harmful chemicals in small quantity, such as heavy metals and chlorinated and fluorinated hydrocarbons.
There is also a widespread problem in modern steelworks in dealing with the steelwork dusts. These dusts contain zinc oxide and spinels which result in the dust being unsuitable for return to sinter plants and from there back to blast furnaces since the zinc content creates problems to upper refractories in the shaft of a blast furnace. A large proportion of modern steelworks dusts are micron-sized particles mainly of iron and iron oxides in which the whole range of valencies of iron are represented. Furthermore the dusts usually contain a variety of calcium-containing compounds, zinc-containing compounds and carbon-containing compounds.
When applied to the treatment of sewage and steelworks dust, the invention is based on the concept of mixing the dusts with sewage, extracting solids and processing the solids in a smelting operation to produce molten iron and a hot gas discharge, the sewage solids including carbon compounds which are a source of carbon in the smelting process for reduction of the iron compounds in the dust and also provide a source of fuel for the smelting operation. However, the invention consists also in a process of separating from sewage solid material as sludge and also in a separate process of smelting sewage sludge.
According to a first aspect of the present invention, there is provided a method of processing sewage comprising mixing steelworks dust into sewage, separating clear effluent to leave sludge, dewatering the sludge and substantially reducing the moisture content of the sludge and producing solid material which can be handled conveniently and is suitable for subsequent smelting to provide valuable metal fractions and to dispose of the organic solids content of the sludge by combustion.
According to a second aspect of the present invention, there is provided a method of treating steelworks dusts comprising taking solid material comprising a mixture of steelworks dusts and sewage sludge, smelting the solid material in a smelt reduction furnace by using carbon-containing compounds in the sludge to reduce metal values in the steelworks dusts and to combust sewage-sourced components in the sludge, and collecting the metal values.
It is particularly advantageous to combine in a process the steps of the first and second aspects of the invention, but it is to be understood that practising either aspect alone is within the scope of the present specification, the process being characterized by interacting steelworks dusts and sewage waste whereby useful material is separated. Furthermore, it is within the scope of the present invention to use some steelworks dusts for settling sewage sludge and to include other materials to aid settling. Additional steelwor
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Patents Abstracts of Japan, C-15, p. 67, 55-49200 Nippon Process Engineering KK, Apr. 9, 1980.
Andrews Melvyn J.
Illawarra Technology Corporation Limited
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