The zinc content of BOF dusts is in a range too high for recycling into the BF, too low for recovering of zinc. Therefore the dust recycling into the converter has been investigated within this project to increase the zinc content to amounts suitable for recovering and due to higher iron contents in the slag to bind free lime contents.
The target of this research has been to investigate the metallurgy of steel and slag during recycling. The quality and properties of the slag, mostly used as aggregates for road construction, must not be influenced negatively.
As a result the tests show that it is possible to recycle BOF dust into the BOF vessel. Zn and other elements easy to be vaporised at steel temperatures will be transferred into the gas atmosphere and will be enriched in the dust. Thus, recycling the dust will increase the contents of valuable elements in the newly formed dust.
The steel quality is not influenced by this recycling. Owing to high bad stirring during the BOF process, all the zinc introduced by the dust briquettes is vaporised during the process. No problems have been encountered during the casting.
Also the quality of the steel slag has not been influenced negatively. The properties of the slag fulfil the demands on aggregates for road construction. Due to higher iron contents in the slag the free lime is bound into calcium ferrites.
The results have advantages for all European steel producer and their processors for the slag. This technique is a further step to produce steel with minimum of residues.