Impact of Pyrolysis Treatment on Heavy Metals in Sediment

Abstract

This paper describes a laboratory study that examined the effect of pyrolysis treatment on the behavior of Hg, Cr, Zn, Pb, Cu and Cd in a stream sediment. The influences of pyrolysis on the evaporation, sequential extraction and leaching behavior of these metals were investigated. Cr, Zn, Pb and Cu were retained quantitively in the solid residue at temperatures up to 800°C while mercury and cadmium were completely or partially evaporated. The metal form distribution in the sludge samples was determined by the sequential extraction procedure. The procedure revealed that as a consequence of pyrolysis, the metals were more strongly fixed in the treated sediment, as could be seen by the decrease with temperature of the first two sequential-extracted fractions and increase of the residue fraction. The leaching results showed that the quantities of the studied metals leached in the two pyrolysis samples were lower than those in the untreated sediment. The amounts of metals leached from the pyrolysis residues correlated significantly with the first extracted fraction (exchangeable fraction).

Keywords:

• evaporation
• leaching
• pyrolysis
• sediment
• sequential extraction

Acknowledgments

The authors thank the New Energy and Industrial Technology Development Organization (NEDO) of Japan for the financial support of this study.

Notes

^avolatile fraction

^bthe Cd in Py800 was calculated as 20.0% in volatile fraction and 80.0% in solid fraction.