LEACHING BEHAVIOR AND SOLID-PHASE FRACTIONATION OF SELECTED METALS ASAFFECTED BY THERMAL-TREATMENT OF A POLLUTED SEDIMENT

A contaminated dredged sediment was subjected to a thermal treatment a t temperatures ranging from 120 to 450-degrees-C. The leaching behavio ur of selected metals (Cd, Cu, Pb, Zn, Fe, Mn) was studied using NH4OA c-EDTA extraction. In addition, solid phase fractionation was carried out by means of a sequential extraction procedure. The NH4OAc-EDTA ext raction showed a sharp increase in metal leachability from sediments t reated at intermediate temperatures (120 - 350-degrees-C). The metal f ractionation 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 o f organic matter at higher treatment temperatures. It is suggested tha t binding energy changes within the fractions rather than shifts betwe en chemical forms account for the observed leaching behaviour.