GB770516A - Improvements in the roasting of comminuted, roastable, sulphur-containing materials - Google Patents

Abstract

Materials containing roastable sulphur, particularly sulphidic ores, which have a grain size such that at least 10 per cent by weight are below 0.3 mm., are roasted in a single fluidized layer consisting predominately of roasted material in which layer a substantial uniform degree of fluidization is maintained. The temperature of the fluidized layer is maintained below 1000 DEG C. and the temperature in the gas space above the layer is maintained above that of the layer either by supplying at least part of the material to be roasted in such a manner as to fall freely into the bed, or by supplying a combustible fuel to and burning it in the gas space, the oxygen content of the reaction gases entering the gas space being correspondingly regulated. Thus sulphidic iron ores may be roasted below 900 DEG C., or zinc containing ores may be roasted above 900 but below 1000 DEG C., the amount of combustible fuel passing into the gas space being regulated such that the temperature in the gas space is about 1100 DEG C. Material to be roasted which contains particles of a grain size from 0.3 to 6 mm. may be fed to the bed by allowing it to trickle from a fall height of at least 1 m. through the gas space, the proportion of grains below 0.2 mm. being chosen so high that the desired rise in temperature in the gas space is obtained. Material which is predominately below 0.3 mm. such as flotation concentrates may be supplied in part directly to the fluidized bed at a point less than 1 m. below the surface of the bed whilst the remainder is allowed to fall into the bed from above to cause the temperature increase in the gas space. The roasted ore dust in iron sulphide roasting is largely Fe3O4.