Study On The Basis Of Vacuum Distillation Of Crude Lead

Crude lead produced by the traditional pyrometallurgy processes usually needs to refine that can be extensively used in lead-acid battery industry, industrial chemicals, anticorrosive materials, etc. Cu, Sn, Ag, Zn, As, Sb and Bi are the common impurities in crude lead. Fire refining process and electrolytic process are normally applied for refining of crude lead. Although both fire refining process and electrolytic process could obtain naturally the requirements to the quality of refined lead, there are some serious problems in conventional refining processes of crude lead. The fire refining process has some disadvantages such as procedure complex, lower direct rate of lead, bad state of operation, evident environmental pollution, etc. The electrolytic process has some disadvantages such as long production period, large investment, high energy consumption, low economic profits, etc. Vacuum metallurgy has many advantages such as short flow, low pollution, low energy consumption, etc. and can eliminate the disadvantages of traditional refining processes. This paper investigated systemically the performance for the refining of crude lead via vacuum distillation to provide a simple, green, efficient and referential way for the removal of impurities from crude lead.This paper introduced concisely the present situation and the development of the refining of crude lead, and discussed the possibility of removal of impurities from the thermodynamics and the kinetics. The removal of impurities from crude lead by vacuum distillation was investigated experimentally.Thermodynamics indicated that Cu, Sn and Ag were concentrated in residue at a higher temperature distillation, and Zn, As and Sb were volatilized into vapor phase and were removed from crude lead at a lower temperature distillation. The impurity Bi was hardly separated at both the high temperature distillation and the low temperature distillation due to the property of Bi was similar to Pb. Kinetics demonstrated that the main influence factors of the evaporation of elements were concentration difference, distillation temperature, melt flow state, evaporation area and system pressure. The order of evaporation velocity of each component in crude lead was:Zn> Sb>Pb≈Bi>Ag>Sn>Cu.The experiment was conducted by the two stage of low temperature and high temperature vacuum distillation and the two stage of high temperature and low temperature vacuum distillation. At the two stage of low temperature and high temperature vacuum distillation, the results showed that the removal rate of Cu, Sn, Ag, Zn, As, Sb and Bi were99.99%,99.5%,98%,0.6%,0.7%,68.19%and1.2%after low temperature distillation at973K for30min when the system pressure was5to15Pa and high temperature distillation at1373K for30min when the system pressure was5to15Pa. At the two stage of high temperature and low temperature vacuum distillation, the results showed that the removal rate of Cu, Sn, Ag, Zn, As, Sb and Bi were99.99%,99.5%,98%,99%,99.9%,86.56%and0.92%after high temperature distillation at1373K for30min when the system pressure was5to15Pa and low temperature distillation at973K for30min when the system pressure was5to15Pa.The total removal rate of impurities for the two stage of high temperature and low temperature distillation was better than the two stage of low temperature and high temperature distillation. The removal efficiency of Cu, Sn and Ag were consistent, but Zn and As were extremely different by the two distillation processes. The great mass of Zn and As were removed from crude lead by the process of the two stage of high temperature and low temperature distillation, but Zn and As were removed scarcely from crude lead by the process of the two stage of low temperature and high temperature distillation. The removal efficiency of Sb for the two stage of high temperature and low temperature distillation was slightly better than the two stage of low temperature and high temperature distillation. The removal of Bi was near by the two distillation processes, and Bi was hardly separated from crude lead by vacuum distillation.