Effect of NaCl on the migration of heavy metals during the non-isothermal and isothermal combustion of sludge: Static and dynamic analyses.

ABSTRACT

Chlorine has been proven to promote the volatilization of heavy metals during sludge combustion. This work compared the migration of heavy metals with NaCl addition under different combustion modes at 900 â„ƒ. The combustion modes have less effect on the mineral phase of residues, but the volatilization and toxicity reduction of heavy metals were more pronounced under isothermal combustion. The mineral evolution, release of Cl, and migration of metals were dynamically tracked by the continuous sampling at different combustion time under isothermal combustion. It was found that the volatile matter and fixed carbon burned almost simultaneously, and the addition of NaCl promoted them. As combustion proceeded, the minerals gradually crystallized and the heavy metals were volatilized due to the direct and indirect chlorination. Meanwhile, the chlorination and volatilization of Zn was less than that of Pb due to its effective solidification by minerals. The combination of the adsorption by exposed char and solidification by sludge minerals influenced the dynamic leaching behavior of metals. These results will help understand the interactions between heavy metals, inorganic Cl, and Fe-Si-Al minerals during combustion, which will further help optimize the combustion strategy for both stabilization or enrichment of heavy metals when inorganic chlorine exists.