Dioxins and furans’ behavior in the process of zinc and lead removing from EAF dust

Abstract

The use of galvanized scrap as a charge material for electric steel-smelting production leads to formation of metallurgical dust suitable for extraction of non-ferrous metals. Chlorine and organic compounds content in metallurgical charge can lead to dioxins and furans formation in the process of electric smelting with their subsequent sedimentation on EAF dust. In the previous study we determined dioxins and furans content in dust at the level of 474 ng/kg of EAF dust. The methodology for conducting an experiment in a muffle furnace at temperatures of 300, 600, 900 and 1150 °Cwas developed for the study of dioxins and furans’ behavior during dust heating. Investigation of EAF dust chemical composition before and after the experiment made it possible to establish that desorption of dioxins and furans occurs during heating in the temperature range of 300 – 900 °C. In parallel with dioxins and furans’ desorption some chemical compounds evaporate indirectly and it is determined by calculation of changes in the content of C, Na, Cl, K, Pb, Zn in the sample. In the studied temperature range, the content of C, Na, Cl decreases to zero; K content is reduced by 81 %; Pb content is reduced by 83.5 %. Reduction of Zn content does not exceed 5 %. Change in content of the remaining components is insignificant. The obtained data confirm the predominant presence of chlorine in inorganic compounds in forms of NaCl and KCl, along with a slight presence in forms of ZnCl, PbCl, and PbCl2 . The study revealed the need of consideration of dioxins and furans’ presence during development of technologies aimed at metallurgical dust processing. It is proposed to perform high-temperature processing of dust (>850 °С) with the subsequent irrigation of exhaust gases with lime milk. The most rational ways to decrease dioxins and furans’ content in EAF dust are conducting afterburning of exhaust gases, followed by rapid cooling in order to avoid secondary synthesis of ecotoxicants or reducing the amount of chlorine-containing and conventional materials during pretreatment of metals.