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Vacuum treatment of iron and steel melts for the removal of copper and tin

The vacuum refining of metal melts is based on the evaporation under vacuum of contaminating solutes which have higher vapour pressures than the vapour pressure of the solvent. The study proved the possibility to refine iron-based melts from copper and tin through the evaporation of these elements. It was found that the main parameters of the refining process are: vacuum level, treatment time, geometry of the melt container, melt temperature, melt composition and degree of mixing. The investigations were performed under an argon atmosphere in a VIM furnace.

The degree of copper or tin removal is not limited if treatment time is sufficient. The melt has to be treated at gas pressures lower than 1 mbar. Good mixing of the melt is necessary for substantial refining. It was observed that the removal rate of tin is very high when carbon-saturated iron melts with high contents of sulphur are treated at 1400 C. In this case tin was removed as the volatile compound SnS.

An advantage of the vacuum refining process is that there is no need for scrap pretreatment (such as electrolytic detinning or extensive shredding and sorting) because the impurities are being removed after smelting of the bulk charge when copper and tin have already dissolved in the melt. Vacuum refining does not cause any process by-products. There is no slag which has to be reprocessed or stored. The impurities which are removed from steel in the form of metal vapours can be condensed and gathered. The obtained material has a high metal value and can serve as raw material for non-ferrous metallurgy. Since vacuum refining is a pyrometallurgical method, it can be put in operation in already existing metallurgical plants without changing to a great extent their technology and equipment.

Reported by

Technical University Bergakademie Freiberg
Leipziger Straße 34
09596 Freiberg
Germany
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