Improvements in or relating to the separation of lead and zinc

摘要

846,152. Distilling zinc. NATIONAL SMELTING CO. Ltd. Sept. 4, 1958 [Oct. 18, 1957], No. 32639/57. Class 82(1) Zinc is separated from zinc of low lead content by distillation under vacuum at a temperature of 450-500‹ C. The zinc of low lead content may be obtained by distillation from zinc-containing lead under vacuum, the vapours being condensed in a circulating stream of molten zinc at a lower temperature, zinc being simultaneously evaporated from this circulating stream and condensed at a still lower temperature. In the apparatus shown m Fig. 1 zinc-containing lead enters by pipe 2 to fill an annular well 3 and overflows lip 7 to flow downwards over the inner surface of wall 5. Zinc vapour contaminated with lead passes to an annular system of shelves comprising outward facing shelves 13 and inward facing shelves 12 over which molten zinc flows from annular trough 17. The vapours condense on the shelves 13 and substantially pure zinc vapour is simultaneously formed by evaporation from shelves 12 to be condensed on a condenser 21 which is cooled by cooling coils 21a to form a solid deposit of zinc 20. At a certain thickness of the deposit 20 the zinc vapour condenses as liquid and drips into tube 25 from which it is withdrawn. The leadcontaining zinc flowing over shelves 12, 13 is collected in annular trough 14a, passes to vessel 14 in which zinc-saturated lead separates and is removed by overflow 18, the remaining zinc being pumped through tube 16 to trough 17. Vacuum is maintained via pipe 24, a cold trap 23 and the interior of condenser 21 in which a radiant heater 22 prevents the formation of accretions of solid zinc. Specifications 685,484 and 711,954 are referred to.