GB971729A - Improvements in the extraction of zinc - Google Patents

Abstract

A finely divided oxidic zinciferous material which is substantially free from volatilizable arsenic and sulphur is obtained from a zinc sulphide concentrate which is heated in an inert atmosphere to a temperature within the range 950 DEG to 1150 DEG C. so as to substantially remove by volatilization any lead, tin, cadmium or arsenic, the resulting zinc sulphide concentrate being then roasted to yield the oxidic zinciferous material. Alternatively, the latter may be obtained from zinc concentrate that has been flash-roasted or oxidized in a fluidized bed. Specification 572,961 is referred to.ALSO:A method of extracting zinc from a finely divided oxidic zinciferous material which is substantially free from volatilizable arsenic and sulphur comprises introducing the zinciferous material and finely divided carbonaceous material into, and entraining them by, a moving stream of an oxygen-containing gas at such temperature that reduction to zinc vapour takes place and all other non-volatile components assume a molten free-flowing form, separating these other components and condensing the zinc vapour to give metallic zinc. The oxidic zinciferous material is preferably obtained from a zinc sulphide concentrate which is heated in an inert atmosphere to a temperature within the range 950-1150 DEG C. so as to substantially remove any lead, tin, cadmium or <PICT:0971729/C6-C7/1> arsenic, the resulting zinc sulphide concentrate being then roasted to yield the oxidic zinciferous material. Alternatively, the latter may be obtained from zinc concentrate that has been flash-roasted or oxidized in a fluidized bed or pulverulent by-products such as flue dusts or granulated lead blast-furnace slags may be used. Copper is preferably present in the zinciferous material which may be in the form ZnO, ZnCO3 or Zn2SiO4, and the zinciferous material and the carbonaceous material may be introduced into the gas stream together or, preferably, separately, one or both being preheated; the material may be dropped in at the top of a furnace or may be injected into a stream of gas in an inlet duct leading to the furnace or into a small proportion of the gas entering the furnace by a subsidiary duct. Alternatively, at least the carbonaceous material may be introduced into the gas stream by a separate entraining stream of nitrogen to obviate ignition due to preheating of the material. A pulverulent flux, e.g. lime and silica, may be introduced into the gas stream. The carbonaceous material is preferably pulverized coke breeze or anthracite dust and should be of low hydrogen content so as to substantially exclude the formation of water vapour. The gas stream is preferably preheated and the relative amounts of oxygen in the gas and oxygen and carbon in the charge should be such as to form a mixture of CO2 and CO having a CO2/CO ratio of 0.6 to 1.6 by volume. In an example oxidized zinc concentrate containing 60% zinc was used with a stream of air preheated to about 600 DEG C. and carbon of about 0.8 times the weight of the zinc. The gas which remained after the zinc had been removed contained about 14% CO2 and 16% CO; the combustion of this gas could be used to preheat the air entering the furnace. The apparatus shown in Fig. 1 which is constructed of specified materials (see Division B2) comprises a cyclone 1 having an air inlet 2 and an outlet throat 3, the cyclone being surrounded by cooling coils 4 and the throat 3 leading to a slag chamber 5 provided with tapping holes 6 and 7 and tuyeres 8 and 9. An offtake 10 leads from the chamber 5 by way of a duct 11 to a condenser system, e.g. a lead-splash condenser of the type described in Specification 572,961. In operation air or oxygen-enriched air, roasted zinc concentrate and pulverized fuel are blown through the inlet 2. The slag runs down the walls of the cyclone into the chamber 5 and is periodically drawn off through the hole 6. Any zinc oxide retained in the slag is reduced by carbonaceous fuel introduced through the tuyeres 8 and 9. The cooling coils 4 may be replaced by a water jacket or water cooled sections in the walls of the cyclone 1. The stream of air in the cyclone may be turbulent.