Leaching Behaviour and Solid Phase Fractionation of Selected Metals as Affected by Thermal Treatment of a Polluted Sediment

Abstract

A contaminated dredged sediment was subjected to a thermal treatment at temperatures ranging from 120 to 450°C. The leaching behaviour of selected metals (Cd, Cu, Pb, Zn, Fe, Mn) was studied using NH₄OAc-EDTA extraction. In addition, solid phase fractionation was carried out by means of a sequential extraction procedure.

The NH₄OAc-EDTA extraction showed a sharp increase in metal leachability from sediments treated at intermediate temperatures (120–350°C). The metal fractionation of the solid phases at the different temperatures did not reveal relevant shifts except for Cu. The decrease of the oxidizable Cu fraction was highly correlated (P < 0.001) with the disappearance of organic matter at higher treatment temperatures. It is suggested that binding energy changes within the fractions rather than shifts between chemical forms account for the observed leaching behaviour.