Complex lead bullions exiting the blast furnace often contain impurities such as silver (Ag), arsenic (As), bismuth (Bi), copper (Cu), antimony (Sb), tin (Sn), and zinc (Zn). Refining of such bullion is traditionally carried out via refining processes such the softening process, and the electrolytic process. Each of these process have disadvantages: the softening is very complex and the operating conditions are not the best; the electrolytic process has a long production time and consumes a lot of energy. Vacuum metallurgy has long been applied to the production of metals such as nickel and tin, and it is known to yield cleaner products, to create less pollution, and to consume less energy. This project will investigate vacuum distillation as an alternative process for the refining these complex lead bullions.
Investigation of vapor pressures for the elements of interest, it can be concluded that pure As, Zn, Sb, and Bi can be removed from pure lead while lead can be selectively removed from Cu, Ag, and Sn. The scope of this project will then be set on the Pb-X alloy systems, X being Ag, As, Bi, Cu, Sb, Sn, or Zn. The effect of system pressure, system temperature, and impurity concentration in the alloy will be evaluated.