Glassification of EAF dust:: The limits for Fe2O3 and ZnO content and an assessment of leach performance

Electric are furnace (EAF) baghouse dust is an environmental problem, both in terms of temporary storage and, ultimately, safe disposal. Vitrification of the dust, so that hazardous components (such as zinc, lead, chromium, cobalt, barium, and arsenic) are incorporated into an amorphous glassy structure, is one option for environmentally benign disposal (and possibly recycling), which is currently being explored commercially, in silica-based glasses at iron levels of up to 15 wt%. However, the ability of vitreous materials to resist leaching of hazardous components may be substantially reduced by components which promote crystallinity, in particular Fe, Zn, Cd, and other transition elements. In the present work the impact of Fe2O3 and ZnO, both individually and in combination, on the vitrification process has been studied experimentally, one objective being to determine the maximum level at which the final product remains essentially amorphous. Several compositions were prepared in the system Fe2O3-ZnO-CaO + MgO + Na2O at 50 wt% SiO2 and 1500 degrees C. Amorphous products were obtained at Fe2O3 levels up to 35 wt%, ZnO levels up to 30 wt% and total Fe2O3 + ZnO levels ranging from 25 to >40 wt% depending on the Fe2O3:ZnO ratio. The addition of minor elements such as Zn, Cd and Pb at levels typical of EAF dust was found to have negligible impact on the ability to form amorphous product structures. Leaching tests carried out on samples showed very low Zn levels confirming the ability of the product from EAF glassification to pass leaching standards which might significantly reduce disposal costs. (C) 1997 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.