SPECIATION OF IRON, ZINC, LEAD AND CALCIUM IN BLAST FURNACE TOP-GAS FILTER DUST BY SEQUENTIAL LEACHING

Top-gas dedusting at blast furnaces (BF) is usually done with venturi scrubbers. However, in recent years, the total dry dedusting of BF top-gas has become a common technology. In this case, a fabric filter is used instead of the venturi scrubber. For recycling, the dry dust from a fabric filter is preferable to the sludge from a scrubber. The main constituents of BF dedusting residues, Fe, C and Ca are of some value, while tramp elements, particularly Zn, can cause problems in the process. Results from leaching of the sludge obtained in wet BF dedusting are available. In contrast, data from leaching of dry filter dust from BF dedusting are not available. However, it has to be assumed that the behavior of a dust from dry dedusting deviates somewhat from that of a sludge due to the prolonged residence time of the sludge in the scrubber system under varying pH. In this study the filter dust of a BF top-gas dry dedusting filter was investigated, applying sequential leaching and X-ray diffraction analysis for the investigation of the distribution of Fe, Ca, Zn and Pb in various compounds with a focus on the tramp element Zn.