On Dioxin Formation in Iron Ore Sintering

Abstract

Iron ore sintering is an important source of "dioxins", polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). This paper reports on attempts to identify materials, conditions, and mechanisms responsible for PCDD/F formation (i) by investigating salient properties of ores (viz., with respect to oxidation, condensation, and chlorination of model organics) and (ii) by mimicking the industrial process on a microscale with real-life materials. Principles of Design of Experiments (DOE) are employed. The reactivities of iron ores differ greatly. Limonite/goethite "soft" ore is a very active oxidation catalyst (e.g., for benzene and phenol), a property that may be useful in cleaning up crude sintering process offgases, whereas hematite/magnetite "hard" ore is not. The latter, however strongly promotes condensation of phenol to dibenzofuran. A newly built lab-microscale sintering facility could satisfactorily imitate the large-scale process, in part or as a whole. Results obtained with realistic feed mixtures point at dioxin formation in the sinter bed at levels significant enough to explain a major part of the outputs observed in the real-life process. With approximately 8 ppm (wt) of chloride added as NaCl, the PCDD/F output doubled, but with the same proportion of chlorine administered as C2Cl4, the dioxin output was over 2 orders of magnitude larger. The use of process reverts, etc. containing chlorinated organics should therefore be avoided. PCDD/F congener patterns are also reported and compared with those observed in practice.

Identification the Content of the Windbox Dust Related to the Formation of PCDD/Fs during the Iron Ore Sintering Process

“…It might be because the involved raw materials for the iron ore sintering process, such as iron ore and return fines, were abundant in both K + , and Na + (Cieplik et al, 2003;Nakano et al, 2005). The above results were also comparable to that conducted by Tsai et al (2007).…”

“…The de novo synthesis has been considered as an important formation pathway of PCDD/Fs during the iron ore sintering process according to the results obtained from several field and laboratory investigations (Kasai et al, 2001a(Kasai et al, , 2001bXhrouet et al, 2001;Cieplik et al, 2003;Kuzuhara et al, 2003;Suzuki et al, 2004;Kasama et al, 2006;Tsubouchi et al, 2006). For example, a series of laboratory sinter-pot studies have identified that the de novo synthesis could be occurred in the drying zone of the sinter bed (Cieplik et al, 2003). More recently, the concept of the two-stage release of PCDD/Fs from the rear half part of the sinter strand has been proposed by Kasama et al (2003).…”

An Overview of PCDD/F Inventories and Emission Factors from Stationary and Mobile Sources: What We Know and What is Missing

“…There is also the presence of chlorine as alkali chlorides and small amounts of Cu in this region (Suzuki et al, 2004). The raw material can contain substances that have been reported to be essential or facilitate the formation of PCDD/Fs e.g., chlorine, organic compounds and metal catalysts like Cu (Cieplik et al, 2003). However, though the current understanding is that PCDD/F are majorly formed within the sinter bed, an analysis of the dust particles in wind boxes revealed that it contains significant amounts of Cl and unburnt carbon (Tsubouchi et al, 2006;Kuo et al, 2011) making it a potential area for PCDD/F formation.…”

Modeling Sintering Process of Iron Ore

“…Finally, this scenario was compared with the actual operation with regard to the emissions of dioxin (PCDD-Poly Chlorinated Di-benzene Dioxin) and furans(PCDF -Poly Chlorinated Di-benzene Furan). The sintering process have been strongly requested to reduce polychlorinated substances emissions, therefore, new technologies need to be compared not only from the point of view of economics but also from the environmental load (Castro et al 2005, Cieplik et al 2003, Kasai et al 2008. Figure 9 and 10 show the comparisons of PCDD and PCDF distributions within the sinter strand for actual operation and case 6.…”

“…The physicochemical and thermal phenomena involved in this process are complex and numerous ( Nakano et al, 2010, Kamijo et al 2009, Kasai et al 2008. Special mention is made to the phenomena of gas flow through the porous bed, gas-solid heat transfer, drying, vaporization and several chemical reactions and phase transformations (Umekage et al 2009, Cieplik, 2003, Cores et al 2010. Several attempts have been done to predict the final properties of the sinter product (Water et al 1989, Kasai et al 1989, 1991.…”