Improvements in or relating to the recovery of zinc from the zinc crust obtained in the separation of silver from lead

摘要

788,525. Distilling zinc; producing lead alloy. SOC. MINIERE & METALLURGIQUE PENARROYA and LEFERRER. F. April 30, 1956 [May 20. 1955], No. 13168/56. Class 82(1) [Also in Group XII] / Zinc crust (an alloy containing Ag. Zn and Pb) obtained in the operation of silver from lead is enclosed in an air tight furnace 6 and its temperature raised to 750- 850‹C. by electric resistors 3. The Zn vapour is conducted through an air tight passage 20 to an air tight condenser 13, the furnace, passage and condenser being maintained at a pressure of 3-12 mm. Hg. The condensed Zn 17 is maintained automatically at a temperature of 420-450‹C. on the one hand by exchange of heat between the furnace, passage and condenser, and on the other hand by a regulating device which is controlled by the condenser temperature, and itself controls the electric resistors. The supply of heat to the alloy is cut off manually or automatically when a sudden rise in furnace temperature to about 1000‹C. indicates that there is no more Zn in the furnace. Substantially pure Zn is collected from the condenser and substantially Zn-free alloy from the furnace. If the zinc crust initially has a melting point above 800‹C., lead is added to reduce it. The regulating device may be a thermo-couple 16 immersed in the condensed Zn and connected by a relay to the electric resistors. The condenser is fitted with a starting heater 15, and the furnace also has a thermo-couple to provide an indication of its temperature. In an example, zinc crust containing 50 per cent Zn, 19.25 per cent Ag, 29.25 per cent Pb and 1.5 per cent Cu was treated to produce Zn containing 1 per cent Pb and 0.15 per cent Ag, and Pb containing 38 per cent Ag, 3.5 per cent Cu, 1 per cent Zn, and 0.5 per cent impurities.