Control of Pb and Cd emission by kaolin during waste incineration

The distribution characteristic of lead and cadmium in PM₁₀ was investigated in a fluidized bed incinerator with kaolin as sorbent to control their emissions. The low pressure impactor (LPI) and atomic absorption spectrophotometer (AAS) were used to detect the size distribution of Pb and Cd in flue gas. The scanning electron microscope/X-ray diffraction/energy disperse spectroscopy (SEM/XRD/EDS) was used to observe the surface morphology and element distribution, respectively. More than 90% of particulate Pb and 85% of particulate Cd in flue gas are enriched in submicron particles. The volatilization of Pb is significantly higher than that of Cd. The reactions of Pb and Cd with kaolin powders can induce the eutectic-melt at high temperature, and its amount increases with the temperature rising. The melted kaolin particles conglutinate to larger particles which can shift the metals in flue gas from the fine to coarse particles. The addition of kaolin can effectively absorb submicron Pb and Cd. The best absorption efficiencies are up to 80% and 50% respectively. For submicron Pb absorption, the optimum incineration temperature is 950 ℃. For submicron Cd absorption, the reaction temperature is much higher; the obvious absorption process occurs until 1 000 ℃.