With the implementation of the new national standards in the steel industry,
dioxins (
polychlorinated dibenzo-p-dioxins (PCDDs) and
dibenzofurans (PCDFs)) emission and control have attracted more and more attention in China. The
PCDD/Fs levels and signatures of nine steelmaking materials and by-products were experimentally analysed and compared, including five kinds of steelmaking
fly ash (sintering
fly ash, basic
oxygen furnace
fly ash, electric
arc furnace
fly ash and two kinds of blast furnace fly), three kind of steel sludge (continuous casting sludge, hot rolling sludge and cold rolling sludge) and sintering raw material.
Dioxin formation from the sintering
fly ash was highest of all 9 materials. Furthermore, highly chlorinated
PCDD/Fs homologues were abundant in that sample, while the profiles were contrary to those of other materials. More importantly, the entire isomer signatures of all 61 samples were analysed, involving various materials, temperatures,
oxygen levels, particle size and inhibitors, with special emphasis on those congeners associated with
chlorophenol precursor routes, as well as seventeen 2,3,7,8-substituted
PCDD/Fs. Strong correlation was found among seven
PCDD-congeners of CP-route. The analysis of the molecular structure of these congeners revealed that 2,4,6/2,3,5-trichlorophenol may act as a precursor to form all those
PCDD-congeners by condensation. In addition, the influence of various factors (temperature,
oxygen level, particle size, inhibitors addition etc.) on the relative importance of CP-route congeners and 2,3,7,8-substituted congeners was discussed, with the goal of shedding more light on the mechanism of
PCDD/Fs-formation.