ABSTRACT
Identification of chemical forms of metals is performed by numerous sequential extraction methods e.g. three-stage extraction procedure BCR. However, many modifications of this method, which were supposed to accelerate the extraction process, made it difficult to compare the results obtained by different researchers. Differences are also found at the stage of preliminary sample preparation for extraction. Sometimes, samples are dried to dry weight before extraction and in other cases they are not dried. So, the results obtained by the same sequential extraction procedure can differ from each other, since the sample structure and type of element bonding with the individual fractions can change during drying. Therefore, the impact of preliminary preparation of sewage sludge samples, consisting in drying the samples to dry weight at 105 °C, on the manner of element binding with the individual fractions was studied. It was found that drying of sludge samples prior to sequential extraction caused immobilization of the elements. Drying of the samples had the greatest impact on Cr, Co, Pb and Ni. It was found that concentration of these elements increased in fraction associated with organic matter in comparison to undried samples.
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