sábado, 20 de marzo de 2010

On Dioxin Formation in Iron Ore Sintering

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 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
Hecho por: Willson Mendoza
C.I: 16.959.604

No hay comentarios:

Publicar un comentario