Separation And Purification Of Complex Tin Alloy By Vacuum Distillation

In recent years, the increasingly complex tin ores have resulted in plenty of complicated tin alloys and low-grade crude tin in the tin smelting process. Meanwhile in the recycling process of tin-bearing secondary resources, a large amount of tin-based alloy materials have been obtained. According to the content and the composition of impurities, tin-based alloy materials can be classified into four categories, tin-lead alloy (Sn-Pb alloy), tin-lead-antimony alloy (Sn-Pb-Sb alloy), tin-lead-antimony-arsenic alloy (Sn-Pb-Sb-As alloy), and crude tin. Traditional pyrometallurgical or hydrometallurgical processes used to separate tin-based alloys may cause such problems as long process flow and environmental protection, etc. It is imperative to develop a common treatment technology to solve the difficult problem of highly efficient and clean separation of tin from such elements as lead, bismuth, antimony, and arsenic, etc.Focused on vacuum distillation theory research and technology development in this thesis, activity and activity coefficient of tin-based alloys are studied and vacuum distillation effects of tin-based alloy are predicted. For the above-mentioned four types of tin alloy, theoretical and experimental research has been carried out on vacuum distillation. Based on the development and industrial application of vacuum distillation equipment, the main conclusions are drawn as follows:(1) Molecular Interaction Volume Model (MIVM) was first used to calculate the component activity of Sn-Sb, Sn-Bi, Sn-Pb alloys at 900-1400℃ and Sn of 10-99%, and the accurate activity data were obtained, which provides a basis for the theoretical research and technological process design of vacuum distillation of tin-based alloys.(2) Theoretical and experimental studies were conducted on vacuum distillation of tin-lead alloys. For tin-lead alloys of any different Pb contents, the Pb content in the tin products can be reduced to 0.003% by three-time vacuum distillation.(3) Theoretical and experimental studies were conducted on vacuum distillation of tin-lead-antimony alloys. The component volatilization ability is as follows:Pb>Sb>Sn in the process of vacuum distillation. For the Sn-Pb-Sb alloy of high antimony (Sb<20%), the antimony content can be reduced to less than 1% by two-time vacuum distillation, from which efficient separation of antimony from the tin-lead-antimony alloy can be achieved.(4) Theoretical and experimental studies were conducted on vacuum distillation of tin-lead-antimony-arsenic alloys. Arsenic in the metal vapor mixture produced from vacuum distillation could be separately condensed. The crude tin with the lead content of less than 0.05%, the antimony content of less than 2%, and the arsenic content less than 0.1% was obtained by the primary vacuum distillation of tin-lead-antimony-arsenic alloys.(5) Theoretical and experimental studies were conducted on vacuum distillation of crude tins. The component volatilization ability is as follows:Pb>Sb>Sn in the process of vacuum distillation of crude tins. Lead and bismuth can be effectively removed by vacuum distillation of crude tins. More than 70% of arsenic and antimony can enter into "open circuits", i.e., about 33.6% of arsenic was collected in a metallic state while about 40% of arsenic went into the product of crude lead.(6) The feeding system, evaporation system, condensation system and discharging system were improved and a new type of vacuum distillation equipment was developed, which helps to achieve automation and continuity of large equipment The technical specifications of the equipment are as follows:the maximum heating power of 230KV, the maximum heating voltage of 32V, the maximum operating temperature of 1500 ℃, the ultimate vacuum pressure of 10Pa and the maximum capacity of 25t/d.(7) The vacuum distillation technology and equipment of complex tin-based alloys were adopted for industrial applications. The content of lead and bismuth is no longer controlled as the indexes of raw materials while the content of antimony can be up to 20%. By the process of vacuum distillation, the impurity contents of lead and bismuth in tin ingots can meet the standard of Sn 99.99A in the GB/T 728-2010. More than 70% of antimony and arsenic can be effectively removed by vacuum distillation and arsenic can be recovered in a metallic state.(8) A new process flow for crude tin vacuum refining was proposed, and pilot production was developed. Compared with traditional pyrometallurgical or electrolytic process of crude tin with higher content of antimony, the total slag rate in the new process can be reduced by 8% and the direct recovery rate of tin increased by nearly 2%. The whole new process is safe and environment-friendly.The technology has a bright future for the widespread in the smelting enterprises dealing with tin, lead and copper, etc., as well as the enterprises with secondary metal resources recovery.