Equilibrium analysis of lead in hazardous waste during co-processing with cement kiln

An equilibrium analysis was performed to determine the migration characteristics of lead under the conditions of sintering in cement kiln and municipal solid waste(MSW) incineration. Using the thermodynamic equilibrium software CHEMKIN, the Gibbs free energy of the reaction system was minimized according to chemical potentials combined with atom population constraints. The results indicate that both chloride and SiO₂ have great effect on the thermodynamic behavior of lead. Chlorides promote the evaporation of lead, while SiO₂ stabilizes lead into silicate. When the incineration temperature in incinerator is higher than 900 K, chlorides mainly exist as HCl. When the sintering temperature is lower than 1450 K, the ratio of HCl to chloride is lower than 50%, and the highest ratio of HCl to total chloride occurs at about 1800 K which is about 80%. Because the main component of cement raw materials is CaCO₃, which generates a large amount of CaO after decomposition, an alkaline atmosphere is generated and the generation of HCl is inhibited. The stabilized rate of lead is 45% in the sintering process in cement kiln, which is much higher than that in the incineration process in incinerator which is only 11%.