Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1994-09-26
1996-08-20
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
75694, 75961, 266145, C22B 702, C22B 1904, C22B 1302
Patent
active
055474900
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method of the kind set forth in the classifying portion of claim 1. It also concerns an installation for carrying out the method, as set forth in the classifying portion of claim 17.
In the production of iron and steel, fine-grain dusts are generated for example in electrical filters for removing dust from the waste gases from converters or in electrical furnaces, the dusts primarily consisting of iron but also containing zinc, lead and alkalies. The disposal of such dusts gives rise to difficulties.
The way of disposing of such residual substances, which in itself is the most obvious method, namely dumping sane, is becoming increasingly difficult for reasons of environmental protection but also because of the steadily increasing costs and the rapidly shrinking capacities of the special waste dumps available. In addition, considerable amounts of iron, zinc and lead are lost as being unused when such materials are dumped.
This situation compelled the industrial circles involved to develop an economic procedure for processing the dusts. On the one hand hydrometallurgical methods are known for processing the dusts, such as alkaline leaching. However, because of the large amount of water used, such methods give rise to problems in regard to waste water and achieve only low space/time yields. On the other hand pyrometallurgical methods are also known. In such methods non-ferrous metals, primarily zinc and lead, and inevitably therewith also chlorides and alkali, are enriched. A number of such methods, for example the plasma method, permits the direct production of zinc and lead metal, with enrichment by non-ferrous metals. In that procedure however chloride waste is produced in a considerable amount, which is very difficult to dispose of.
At the present time a combination of the rolling method and the imperial smelting method is the most widely used procedure for processing of the dusts.
In the known rolling method, a mixture of sand, coke and foundry dust is continually introduced from one side into a slightly inclined, slowly rotating rotary cylindrical kiln or furnace. Hot air is fed in a controlled fashion from the other side. In the rotary cylindrical furnace, vapours issue from the mixture at a temperature of about 1250.degree. C. and oxidise in the atmosphere in the furnace in order inter alia to form zinc and lead oxides. Those oxide vapours are passed to a cooling apparatus and are cooled down therein and are then passed to an electrical separator where the rolled oxide containing lead and zinc is separated off.
Preferably the oxide is then briquetted and then subjected, together with a reducing agent, in particular coke, to the known imperial smelting procedure. In a blast furnace which then contains rolled oxide and coke, both zinc vapour and also crude lead are obtained and slag is produced. The zinc vapour is passed out of the blast furnace to a condenser where it meets an intensive shower of lead drops and there condenses. In that case the resulting lead-zinc solution is continuously pumped into a cooling system where it is cooled down; the crude zinc which is accumulated in the cooling procedure below the saturation limit on the surface of the lead is tapped off and the remainder, therefore essentially the lead, is fed to the spray condenser again.
Although high levels of through-put can be achieved with the rolling method and zinc and lead can be recovered from the foundry dust in the subsequent imperial smelting method, the installations required for the respective procedures are highly cost-intensive. In order to be able to work economically, they must always be operated in a fully extended fashion. In that respect considerable transportation costs are incurred in bringing the foundry dusts from the individual steel works to the rolling installation and then taking the rolled oxide to the central imperial smelting installations. Transportation is made more difficult by dioxin and furan contents which are possibly present in the material to be processed.
It has been fou
REFERENCES:
patent: 2045639 (1936-06-01), Eulenstein et al.
patent: 4673431 (1987-06-01), Bricmont
Banski Hans
Discher Heinz-Peter
Greinacher Ekkehard
Andrews Melvyn
Sudweststahl GmbH
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