Methods of increasing the rate of tin evaporation from iron-based melts

The low evaporation rate is a main obstacle to the large scale application of vacuum refining of steel scrap melts with respect to tin. In this paper several possibilities of increasing the evaporation rate of tin have been i nvestigated. Iron-based melts containing 0.3 to 0.6 mass% Sn were treated i n a laboratory-scale vacuum induction melting furnace at a pressure of 10 P a. (1) It was confirmed that detinning is enhanced by increasing the sulphur c ontent of liquid iron. This effect is explained by the evaporation of volat ile SnS. The kinetics of SnS evaporation is discussed. (2) Evaporation of volatile SnO from steel melts containing less than 0.024 mass% oxygen was not confirmed. (3) The highest evaporation rate of tin in elemental state is observed from high-silicon iron melts. The most favourable conditions occur at approxima tely 22 mass% Si in the iron melt. This fact is discussed in terms of the t hermodynamics of the liquid Fe-Si-Sn system. (4) New process schemes of tinplate scrap recycling are considered. It is s uggested to use tinplate scrap as iron-bearing material for the production of ferro-silicon alloys. The recycling of tinplate scrap in the ferro-silic on production has potential benefits over its recycling in steelmaking. (5) It is demonstrated that the condensate gathered during vacuum refining of tinplate scrap melts can be reprocessed in the non-ferrous industry to o btain pure tin.