Characterisation of dusts and sludges generated during stainless steel production in Brazilian industries

During the stainless steel production process, wastes are generated at the electric arc furnace (EAF) and at the converters. These wastes are a problem for stainless steel industries, for they must be disposed of in controlled landfills. Finding areas to make more landfills is becoming difficult, and new landfills are being placed far from the industries. This leads to an increase in disposal prices and, furthermore, in production prices. Recycling of these wastes, besides solving the disposal and environmental problems, makes it possible to recover valuable metals such as iron, chromium, and nickel. These three metals are needed in stainless steel manufacture and could be returned to the production procedure, hence bringing profit to the industry. It is important, therefore, to develop a recycling process. Waste characterisation is an essential step in the definition of such a process. Four kinds of dust and two kinds of sludge, generated in stainless steel production, were characterised in the present work. The techniques used to characterise the waste were chemical analysis, size separation, density measurement, X-ray diffraction analysis, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) microanalysis. The largest proportion of the dust and sludge particles was of spherical shape. This kind of particle was composed mainly of iron and chromium in the form of a spinel, or of oxides. Precipitation of a secondary phase was identified in some particles.