Lead Production
Lead Production
Oxidizing roasting of PbS with following reduction of PbO obtaining crude lead ("bullion") followed by refining (purification) of it is the main way of lead production. The roasting is processed in sinter pallet continuous-type machines. The main roasting reaction is:
2PbS + 3O2 = 2PbO + 2SO2.
Some amount of lead sulphate PbSO4 is transferred into silicate PbSiO3 by adding some quartz sand into the furnace-charge. At the same time sulphides of other metal impurities (copper, zinc, and iron) are also oxidized. As a result of roasting agglomerate, a porous sintered mass, consisting mostly of PbO, CuO, ZnO, Fe2O3, is obtained instead of powder mixture. The pieces of agglomerate are mixed with coke and limestone, after which a water-jacket furnace is loaded by this mixture which is blown through by compressed air delivered from the bottom piping ("tuyere"). Lead is reduced from PbO by coke and carbon monoxide at relatively low temperatures up to 500°C. Copper and iron impurities are removed by liquation. Tin, arsenic, antimony are eliminated by air blast through the molten metal. Silver and gold are extracted by adding zinc which forms silver-gold-zinc crust consisting of metals with less weight than lead and melting temperature at 600-700°C. Surplus of zinc is removed from molten lead by air, water vapour or chorine blasted through. Bismuth is removed by adding calcium or magnesium which form high-melting compounds Ca3Bi2 and Mg3Bi2. Lead obtained by this method has 99.8-99.9% purity. Further purification is performed by electrolysis after which 99.99% purification may be reached.