ATMOSPHERIC EMISSION OF DIOXINS AND RELATED COMPOUNDS FROM IRON ORE SINTERING PROCESSES

The sintering processes in integral cycle steel plants are the primary source of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/Fs). Iron sintering is a high temperature agglomeration process that was developed to obtain a product suitable for blast furnace feedstock. This process has undergone several evaluations to define under which conditions dioxins and furans are generated. These assessments are extremely important both for the reduction of atmospheric emissions and for understanding the type of compounds emitted which are important from a toxicological point of view. This paper provides a review of technical information on the formation and reduction of dioxins/furans emissions from iron sintering plant of Taranto (Southern Italy) including a discussion on the sintering process, the dioxins/furans formation, emission control and pollution prevention techniques. The processes by which dioxins/furans are formed are not completely understood. According to heterogeneous mechanisms, PCDD/Fs are formed through the two pathways: (a) de novo synthesis, starting from macro-molecular carbon or polycyclic aromatic hydrocarbons (PAH) and (b) condensation reactions starting from molecular rearrangement of precursor compounds, such as chlorinated phenols. Both paths proceed on the surface of carbonaceous particles in the presence of chlorine compounds and metal catalysts. Various technologies have been tested in recent years for the reduction of emissions, such as for example injection of coal dust upstream of the electro filters or addition of amines (eg urea) in the agglomeration mixture. The evaluation of PCDD/Fs congeners fingerprint indicates a greater presence of chlorinated furans compared to dioxins. The examination of these fingerprints is an important point to evaluate the influence of emission sources on environmental contamination, even if diffusion and transport processes can alter the distribution of congeners in the various matrices.