Abstract: The thermodynamic equilibrium model were applied to predict the transformation of lead during the sludge incineration and the adsorption effects of Pb by four sorbents(Al₂O₃, SiO₂, TiO₂ and CaO) were simulated with the minimized Gibbs free energy approach. The interaction between Pb and sulfur, chlorine, together with the reaction between sorbents and Pb caused by sulfur and chlorine were considered in this procedure. The result showed that the transformation of Pb was affected greatly by sulfur, chlorine and minerals. At low temperature the lead existed in the form of PbSO₄(solid) under the presence of sulfur, while it changed into PbO(gas) at high temperature.The Pb was volatized because chlorine was easy to combine with Pb forming the metal chloride with low boiling point, and the increase of chlorine could speed up the volatilization of Pb. The four sorbents mentioned above were able to remove Pb in some degree. Al₂O₃ could capture Pb in a wide range of temperature, while CaO was not so good. Because sulfur and chlorine had stronger reaction with Pb, they restrained the reaction between sorbents and Pb, during which effective temperature area was narrowed, adsorption rate was reduced, and even Pb removal ability was lost. The effect of chlorine appeared much more than that of sulfur.

Key words: Sewage sludge, Incineration, Pb, Speciation, Sorbent, Thermodynamic equilibrium