Dioxins and furans in zinc-containing metallurgical dust: behavior and formation processes

The use of galvanized scrap as a charge material for electric steel-smelting production leads to the formation of metallurgical dust suitable for the extraction of non-ferrous metals. The issues related to the behavior of chlorine and its compounds in zinc and lead containing EAF-dust is not sufficiently studied. Current research exhibits the danger of chlorine and its compounds in charge and, consequently, in emissions of EAF. Chlorine and its compounds are considered to be the main components associated with the formation of highly toxic organic substances – dioxins and furans (D&F). D&F enter the environment not only in gaseous form, but also in the form of compounds adsorbed on the surface of dust particles. According to various data, D&F concentration is 5-500 ng / kg of dust and depends on the technological parameters of melting. Analysis of the formation processes of D&F in EAF and their behavior in the captured dust is given. It was found that at the studied chlorine content of 1.3% in EAF-dust from the charge materials, 99.9% of chlorine form relatively safe compounds, mainly chlorides, and a small amount goes to the formation of D&F. The amount of D&F adsorbed on the surface of captured dust particles was 474 ng / kg of dust. As strong toxicants, D&F increase the hazard category of dust from the 4th to the 3rd and above that must be considered at dust usage. In addition, the transport of D&F in the environment is due to solid particles that absorb poisons on their surface. Therefore, EAF dust, with D&F adsorbed on its surface, can provoke their entry into organisms. The ways of reducing D&F emission in the production of EAF-steel and the resource-saving and environmentally safe technologies of dust processing are considered. In particular, the possibility of using lime milk for the off-gases irrigation in the EAF gas flue was analyzed and it was shown that it allows to reduce the D&F content to acceptable limits. The efficiency of the proposed activities was evaluated.