2000 Volume 40 Issue 7 Pages 654-663
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 investigated. Iron-based melts containing 0.3 to 0.6 mass% Sn were treated in a laboratory-scale vacuum induction melting furnace at a pressure of 10 Pa.
(1) It was confirmed that detinning is enhanced by increasing the sulphur content of liquid iron. This effect is explained by the evaporation of volatile 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 approximately 22 mass% Si in the iron melt. This fact is discussed in terms of the thermodynamics of the liquid Fe–Si–Sn system.
(4) New process schemes of tinplate scrap recycling are considered. It is suggested to use tinplate scrap as iron-bearing material for the production of ferro-silicon alloys. The recycling of tinplate scrap in the ferro-silicon 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 obtain pure tin.