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Investigation of the contamination of a fly ash sample during sample preparation by air classification
Lanzerstorfer, C.
Abstract
Information on the size dependence of the
concentration of pollutants in fine-grained residues is
required for the design of classification processes for
their processing. For such an analysis, the samples have
to be classified prior to chemical analysis. Depending on
the particle size range of the residue, a classification
method has to be selected. For very fine material, air
classification is a suitable method. In this work, the
results of the classification of fly ash from a biomass
combustion plant with an air classifier are discussed with
respect to the observed sample contamination. The
chemical analysis of the produced size classes for heavy
metals yielded unexpected results. For most heavy metals,
the mass balance resulted in a recovery rate of about
100 %; however, for Cr and Ni, the recovery rate was
way above 100 %. A more detailed analysis of the data
revealed that the ratio of the excess of Cr to Ni in the
fly ash was nearly the same as the ratio of Cr to Ni in
the material of parts of the classifier. Therefore, erosion
of some material from the classifier can be assumed to
have caused the contamination of the sample. For the
classification of samples, which have to be analysed for
Cr and Ni, a classifier has to be used which is made of a
material other than stainless steel.
Keywords
Dust sample; Sample preparation; Classification; Heavy metal contamination
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