Characterization of basic oxygen furnace dust and zinc removal by acid leaching

The basic oxygen furnace (BOF) sludge samples received from Dofasco Inc., have been characterized by a variety of methods such as X-ray diffraction, chemical analysis, particle size and scanning electron microscope and energy dispersive X-ray analysis. This characterization phase was accompanied by experimental work to see to what extent the zinc-bearing components would be removed. The experimental work involved various methods such as scrubbing and size separation, flotation, and size separation followed by sulphuric acid leaching. Physical separation methods were found to be largely inappropriate for this kind of complex material. Chemical processing has a much greater chance of success. It was demonstrated that about 81% of zinc could be removed from the coarse size fraction (i.e., >38 mum) of the BOF sludge sample by sulphuric acid leaching at a pH of about 2. The corresponding amount of iron co-extracted by acid leaching was about 18%. This leaching step lowers the zinc content of the iron-bearing solids to 0.39%, a product which is acceptable for its recycling to the main iron-steel making process. Based on the current findings, a simple classification and leaching circuit was proposed to produce an acceptable product suitable for recycling. The fines fraction does not seem to be amenable to separation by either physical or chemical methods that have been examined so far. The amenability of coarse fraction to processing may represent a partial solution to this problem. However, it seems to offer highly significant financial saving due to avoidance of corresponding land-disposal costs. (C) 2003 Elsevier Ltd. All rights reserved.