GB989704A - Process for the production of zinc calcine - Google Patents

Abstract

<PICT:0989704/C1/1> Zinc oxide is produced from zinc sulphide ore by a process comprising maintaining, at 815 DEG to 900 DEG C., preferably 845 DEG to 870 DEG C., a fluidized bed containing particles of partially roasted zinc sulphide ore finer than 100 mesh and particles of substantially completely roasted zinc sulphide ore larger than 100 mesh, introducing zinc sulphide feed ore containing iron and having particles both finer and coarser than 100 mesh, into the bed at a point below the top surface and 6 inches to 3 feet above the bottom surface of the bed, passing a free oxygen-containing gas, preferably air, up through the bed to maintain the bed in fluidized condition, in amount at least sufficient to convert the sulphide ore to the corresponding oxide, to partially oxidize the feed sulphide ore and to entrain and carry out of the bed as a suspension partially roasted particles of ore finer than 100 mesh in an amount more than 50% (preferably more than 90%) of the ore fed to the fluidized bed, passing this suspension in the gas from the top of the bed through a free space maintained at 815 DEG to 985 DEG C., preferably 870 DEG to 955 DEG C. and having a volume at least seven times, preferably 10 to 20 times, the volume of the fluidized bed, to effect substantially complete oxidation of the suspended ore, discharging the zinc calcine and gas from the free space and separating the roasted ore particles from the gas, at least in amount of 75%, preferably in excess of 90%, while maintaining a temperature of at least 790 DEG C. (preferably 815-930 DEG C.) prior to, and during, separation. The separated roasted particles can then be discharged from the separator, and the gas cooled, e.g. by means of a waste heat boiler, and the remainder of the fine particles of dust in the gas recovered, preferably by a hot gas electrostatic precipitator. The temperature in the fluidized bed may be controlled by the introduction of water or waste acid, and that of the free space above the bed by recycling cooler gas or by spraying liquid into the top of the reaction chamber or by a combination of these methods. As shown, feed ore passes into fluidized bed 4, from bin 1. Air, at a velocity of 75-105 cm. per second passes upwardly through distributer plate 5, and bed 4. The entrained, partially roasted ore solids in the gas pass upwardly from bed 4 to free space 12 wherein oxidation continues. The suspended roasted particles and gas leave roaster 11, through 17, to dust collector 18, wherein most of the solid particles are separated, and discharged through 21. The gas containing minor amounts of flue dust passes to waste heat boiler 23 via 22, to cool the gases to 260 DEG to 370 DEG C. Any particles which deposit are discharged through 27 via 25 and 26 to storage. The cooled gases pass to hot gas electrostatic precipitator 31, to remove the last traces of fine particles of dust entrained by the gas, the dust being discharged through 34. The purified cooled gas containing SO2 may be directed via 35 to conventional contact process for conversion to sulphuric acid. A portion of the cooled gas may be returned to free space 12 of roaster 11. The recovered zinc calcine may be collected separately, or combined to pass through 37 to cooler 38. The larger particles in roaster 11 accumulate in bed 4, and may be discharged through 16.