| Tin is a valuable metal, its reserves is1.6×106t in China, but high grade tin ore is not common now. The tin content the majority of ore is only1%or less, so it is particularly urgent and necessary to recycle tin resources. The valuable tin secondary resources include tin plate and tin slag, in essence, they are both iron-based alloys containing tin. The traditional methods of recycling tin resources have shortcomings, such as longer process, consumption of chemical reagents is much, utilization is not high. Because of the method of vacuum metallurgy has many obvious advantages:shorter process and less polluting, the author try to recycle tin efficiently from iron-based alloys containing tin by vacuum distillation.Firstly, the article gives a general comment on the present situation and the development of recycle tin resources, and discussed the possibility of separation of alloys from the thermodynamics and kinetics. Finally, in a vacuum induction furnace and distillation vacuum furnace, separation of tin slags and Sn-Fe alloys by vacuum distillation were investigated experimentally.Thermodynamic and kinetics calculations indicate the following:the volatile order of three element is As, Sn, Fe. P*As/P*Sn is1.47×1010-2.71×107at873K-1173K, and P*Fe/P*Sn is2.7×10-2-5.3×10-2at1673K-1973K., so As and Sn will volatilize into gas phase, Fe remain in liquid phase at a given temperature. Through the analysis of binary phase diagram, it can be seen that lots of intermetallic compound, which will slow down the spread of As and Sn atoms in liquid alloy, so distillation temperature must above the melting point of intermetallic compound which has the highest melting point, and it is1303K. The main influence factors of the evaporation rate of elements are concentration difference, temperature, melt flow state, specific surface area of volatile surface, pressure.From the experiment of separation of Sn-Fe alloys contain4.54%Sn by vacuum distillation in vacuum induction furnace, it can be informed as follows:distillation temperature and distillation time had significant effect on the removal rate of Sn. With the extension of distillation time and the rise of temperature, the removal rate of Sn and Fe content in residues both increased. Pressure had little effect on the removal rate of Sn when pressure was limited in the range of0.1Pa-10Pa. The removal rate of Sn was99.79%and Sn content in residues was0.024%when Sn-Fe alloys was distilled for42.5minutes at1885K and lOPa. Electromagnetic stirring had significant influence on the separation of Sn-Fe alloys.From the experiment of separation of tin slag contain5.82%Sn by vacuum distillation in vacuum induction furnace, it can be informed as follows:Sn content in residues was0.024%when the slag was distilled for20minutes at60KW and10Pa in vacuum induction furnace, and most of tin volatilized into gas phase, Sn content in condensate was69.8%. And part of As and S volatilized into gas phase.From the experiment of separation of tin slag contain35.42%Sn by vacuum distillation in vacuum induction furnace, it can be informed as follows:the removal rate of Sn increased as distillation power increased when the slag was distilled for30minutes at10Pa. Sn content in residues was14.49%when the slag was distilled three times.From the experiment of separation of tin slag contain35.42%Sn by vacuum distillation in vacuum distillation furnace, it can be informed as follows:Sn content in residues reduced, Fe content in residues increased and the removal rate of Sn increased with the extension of distillation time. Sn content in residues was0.38%, Fe content in residues was76.92%and the removal rate of Sn was99.57%when the slag was distilled for360minutes at1873K and10Pa in vacuum distillation furnace. With the extension of distillation time, more and more Fe volatilized into gas phase. |
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