Study of the Behavior of Dioxins and Furans in the Zinc and Lead Removal Process from EAF Dust

Resumo

The use of galvanized scrap as a charge material in electric steelmaking results in metallurgical dust formation suitable for nonferrous metal extraction. The chlorine and organic compounds content in metal charge can lead to dioxins and furans formation during electric smelting with their subsequent sedimentation on EAF dust. In a previous study, the authors found dioxins and furans content in dust at 474 ng per kg of EAF dust. To study the behavior of dioxins and furans during dust heating, a procedure was developed for conducting an experiment in a muffle furnace at temperatures of 300, 600, 900, and 1150°С. A study of the chemical EAF dust composition before and after the experiment has shown that, upon heating, the dioxins and furans desorption runs in the temperature range 300–900°C. In parallel with dioxin and furans desorption, the evaporation of certain chemical compounds occurs and indirectly causes a dioxins in the C, Na, Cl, K, Pb, Zn content in the samples. In the studied temperature range, the content of C, Na, Cl decreases to zero; K content is reduced by 81%; Pb—by 83.5%. The zinc reduction does not exceed 5%. The data obtained confirm the predominant presence of chlorine in inorganic compounds in the form of NaCl and KCl, along with an insignificant presence in the form of ZnCl, PbCl and PbCl₂. The study shows the need to take into account with the presence of dioxins and furans when creating procedures aimed at EAF dust processing. High-temperature dust treatment (>850°С) followed by irrigation of exhaust gases with lime milk is recommended. Thus, exhaust gases afterburning followed by rapid cooling to avoid secondary ecotoxicant synthesis or reducing the amount of chlorine-containing and organic substances during preliminary metal charge preparation techniques may be considered as the most efficient approaches to reduce dioxins and furans emission.