Chemical Dissolution of Lead Blast Furnace Accretions with Potassium Carbonate in the Presence of Carbon

AbstractIn the conventional production of lead bullion, the sinter, primarily lead oxide, is mixed with coke (about 10% of the charge, by weight) and a small amount of scrap iron, which serves to reduce any lead sulfide present, and then charged into the lead blast furnace. Lead oxide is reduced to metal which collects in the furnace crucible. Zinc oxide in the charge tends to dissolve in the molten slag which contains 30–40% SiO2, 25–40%; iron oxides, the balance being CaO and ZnO. The zinc-content may be as high as 20%.At the high operating temperatures of the lead blast furnace (> 1000°C), the dissolved zinc oxide in the slag is reduced to zinc vapor.ZnO(slag) + C(s) = Zn + COZnO(slag) + CO = Zn + CO2.The zinc vapor in the ascending gases readily reacts with any lead sulfide in the charge as follows:Zn + PbS(s) = ZnS(s) + Pb(1).The solid zinc sulfide, a relatively high melting substance with low vapor pressure, will deposit and accumulate on the furnace walls.