GB438451A - Improvements in and relating to the roasting of ferruginous sulphide ores - Google Patents

Abstract

Ferruginous sulphide ores are roasted by being passed in co-current flow with gases containing oxygen, not more than 70 per cent nitrogen, and at least 10 per cent sulphurdioxide, whereby p non-ferrous metals present are converted to sulphates. The gases leaving the ore should contain free oxygen to ensure complete desulphurization of the iron, and the gases leaving the furnace may be recirculated after suitable concentration in respect of sulphur dioxide. The ore may be given a preliminary roasting treatment in countercurrent flow with a mixture of air and concentrated sulphur dioxide, and the gases leaving the countercurrent treatment be cooled to condense sulphur and be added to the gases leaving the co-current treatment, the mixed gases, or a part thereof, being treated to remove all or part of the nitrogen, together with any carbon dioxide, and the concentrated gases, or a part thereof, being divided into two portions which are returned respectively to the countercurrent and co-current roasting steps. By mixing carbonaceous fuel with the ore prior to the countercurrent roast, substantially the whole of the sulphur removed from the ore may be recovered as free sulphur. Any excess of sulphur dioxide in the circulating gases may be removed from the process and utilized, for example, for the production of sulphuric acid. The countercurrent roast may be effected at 900 DEG C., and the sulphating roast at 800 DEG C. Specifications 353,861 and 394,650 are referred to.