Formation of PCDD/Fs in the sintering process: influence of the raw materials.

The sintering process is among the major sources of PCDD/Fs in the environment. This research studies the influence of the raw materials in this type of industrial plant on the amounts of PCDD/Fs generated. Particular interest is given to coke, which constitutes the principal source of carbon for the de novo synthesis of PCDD/Fs, and to the dust collected in the electrostatic precipitator (E.S.P. dust), usually recycled in the raw materials. The de novo synthesis of PCDD/Fs is simulated at the laboratory scale by thermal treatments of the samples. The use of a particular coke as a fuel does not drastically reduce the formation of PCDD/Fs. Actually, the global amounts of PCDD/Fs generated from the graphite and the two cokes tested are very similar. Only modifications in the fingerprint are observed. On the other hand, the addition of 10 wt % dust collected in the electrostatic precipitator leads to the formation of amounts of PCDD/Fs multiplied by a factor larger than 10(3). These results imply caution against the recycling of this E.S.P. dust in the raw materials.