Chemical characterization of dust particles recovered from bag filters of electric arc furnaces for steelmaking: Some factors influencing the formation of hexachlorobenzene

To make clear some factors controlling the formation of hexachlorobenzene (HCB) in the process of electric arc furnace (EAF) steelmaking, six dust samples recovered from different bag filters in commercial EAF steelmaking plants have been characterized with XRD, SEM-EPMA, XPS and temperature-programmed desorption (TPD) techniques. These dust samples contain 1.9-8.0 mass% of chlorine element, and the XPS and TPD measurements exhibit that the Cl is enriched at the dust surface and composed of the inorganic and organic functionalities, part of the Cl being evolved as HCl in the temperature region of flue gas treatment. All of the samples also include 2.1-6.4 mass% of carbon element, and some of the C can release CO2 in the TPD up to 300 °C to form active carbon sites. The number is related closely to HCB concentration of each dust. Further, it is suggested that the Zn present in the samples consists of ZnFe2O4, ZnO and surface ZnCO3, and the dust with a larger content of the ZnCO3 has a higher concentration of HCB. It is possible that HCB formation occurs via gas-solid-solid interactions among gaseous Cl-containing compounds in flue gas, active carbon sites and surface Zn-species produced in exhaust ducts and bag filters.