Adsorption Mechanism of Heavy Metals on Sorbents during Incineration

This study investigated the adsorption mechanism of heavy metals Cr, Cu, Pb, and Cd on the sorbent during incineration by the following technologies: (1) thermal desorption of heavy metals from the sorbent; (2) identification of heavy metal species in the adsorbed sorbent by x-ray diffraction technique; (3) thermodynamic equilibrium simulation of heavy metals and sorbent; and (4) micrography of the sorbent by scanning electron microscopy. Experimental results indicated that adsorption mechanism of heavy metals on sorbent is related to the volatility of heavy metal species formed at high temperatures and the chemical reactivity with the sorbent. For less volatile heavy metals Cr and Cu, chemical reaction is the major adsorption mechanism, and particle growth due to condensation, coagulation, and sedimentation will become important as the reacting time is increased. For highly volatile metal Cd and most metal chlorides, physical molecular adsorption and particle growth processes are the major mechanisms. Most volatile metal species are adsorbed/distributed on the surface of the sorbent. For Pb (which has been classified as medium to high volatility), chemical and physical adsorption mechanisms are all-important depending on the reacting environment.