THE BEHAVIOR OF HEAVY-METALS AND PHOSPHORUS IN AN ASH MELTING PROCESS

In this study, the bottom ash from wastewater treatment sludge was exa mined to investigate the behavior of heavy metals and phosphorus in th e melting process by a lab-scale as well as a pilot-scale experiment. The lab-scale experiment was performed in air or argon at temperatures from 800 to 1500 degrees C using an electric furnace and crucibles. T he proportions of heavy metals remaining in the slag after the melting were effected by the compositions of the ash, especially basicity (Ca O/SiO2). The proportion of Cd, Pb, Zn and Cu in the residue increased with the elevated basicity. Phosphorus did not volatilized by the melt ing process, and remained as a stable form, Ca-3(PO4)(2) by conjugatin g with Ca. Pilot-scale tests were also performed using swirling type m elting furnace at 1400 degrees C. The volatile heavy metals, like Cd, Pb and As were found in the dust collected by ceramic filter, whereas Zn, Cr and Mn were combined into the slag by the melting process. (C) 1997 IAWQ. Published by Elsevier Science Ltd.