The present study describes the formation mechanisms and leachability of Cr(VI) from electric furnace dust and filter cake from the ferrochromium and stainless steel industries. The results show that stainless steel dust is formed by the entrainment of charge materials, volatilisation of elements and ejection of slag and metal by spitting or bursting of gas bubbles. Ferrochrome dust is formed by the ejection of slag and metal from the electrode holes, the entrainment of charge fines, vaporisation as well as the precipitation of reaction products in the off gas duct. Toxicity characteristics leaching procedure (TCLP) and American Society for Testing and Materials (ASTM) D3987–85 tests show that these wastes are all hazardous materials according to South African legislation, owing to the high degree of Cr (VI) leachability. Cr(VI) in the wastes is easily leached by distilled water, and cannot be stockpiled without prior treatment.
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