GB809765A - Improvements in roasting zinc sulfide ores - Google Patents

Abstract

Cadmium, lead, arsenic, antimony, tin, germanium, and mercury sulphides are removed from finely-divided zinc sulphide ore concentrates by agglomerating the concentrate into particles between 4 and 65 mesh (Tyler), charging the agglomerates into the upper portion of a columnar fluidized bed and introducing air into the lower portion of the fluidized bed in an amount at least 5 per cent, preferably 15-35 per cent, in excess of that theoretically required to combine with the zinc sulphide component of the charge. This air also fluidizes the bed. A gaseous fuel in amount at least sufficient to consume the excess air is introduced into the upper part of the bed, but a substantial distance below the surface, thus maintaining in the upper part of the bed an atmosphere non-oxidizing with respect to the sulphides. The bed is maintained at at least 900 DEG C., preferably between 900 DEG and 1100 DEG C., by recycling some of the roasted ore, or by immersing water coolers in the bed. Roasted zinciferous particles are withdrawn from the bottom of the bed, and roaster gases containing the volatile sulphides, as enumerated above, and the sulphur values from the zinc sulphide as SO2, are withdrawn from the top of the bed. A small proportion of the roasting air may be used to purge the zinciferous particles as they are withdrawn before it enters the bed. The term gaseous fuel includes liquid fuels which are gaseous at the temperature of the bed. The fuel may be natural gas, refinery cracking gas, butane, or a gas such as producer or coal gas, or a vaporized fuel oil by charging fuel oil directly into the column. In an example, zinc sulphide concentrates are agglomerated with bentonite, sulphite liquor, and water, dried and roasted, as described above. Specification 661,560 is referred to.