Effects of Chlorine and Phosphor on Zinc Transformation Behavior During SewageSludge Combustion

Abstract

Effects of chlorine and phosphor on the transformation of zinc during combustion of sewage sludge (SS) was investigated by two approaches: combustion experiment and thermodynamic simulation. The result of thermodynamic simulation predicted that zinc existed as ZnSO4 (s) below 400°C, while mainly as phosphate in solid phase when the combustion temperature was in the range from 500–1200°C but was released as metallic vapor at higher temperatures (>1300°C). NaZnPO4 and Zn(PO3)2 were experimentally detected by X-ray diffraction in sewage sludge slag (SSA) at 900°C. The volatilization rate of zinc was below 10.00% in all cases, and increased slowly along with the combustion time and temperature. However, this volatilization rate significantly increased with chlorine addition through the formation of metal chloride, while phosphor additives restrained the volatilization of zinc.