In this study, the bottom ash from wastewater treatment sludge was examined to investigate the behavior of heavy metals and phosphorus in the 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 °C using an electric furnace and crucibles. The proportions of heavy metals remaining in the slag after the melting were effected by the compositions of the ash, especially basicity (CaO/SiO2). The proportion of Cd, Pb, Zn and Cu in the residue increased with the elevated basicity. Phosphorus did not volatilized by the melting process, and remained as a stable form, Ca3(PO4)2 by conjugating with Ca. Pilot-scale tests were also performed using swirling type melting furnace at 1400°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.

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