Research Of The Ca/Si Influence On Heavy Metals' Volatilization In MSWI Fly Ash Thermal Treatment

Hazardous wastes that contain heavy metals distribute widely with a large quantity, 18 kinds of which are contained in the hazardous waste list of China. Municipal solid waste incinerator (MSWI) fly ash is defined as a hazardous waste for it's containing of high leaching ratios of heavy metals and high toxicity of dioxin, so it must be treated and disposed appropriately. Thermal treatment with the advantages of marked weight-reduction, high stability and resource-recycle is becoming a new significant research in MSWI fly ash treatment community. The high content of calcium and silicon in MSWI fly ash and Ca/Si is an important infection for heavy metal'volatilization, so it has outstanding meaning to research the volatilization of heavy metals with different Ca/Si during the thermal treatment process. The paper studied the volatilization of heavy metal in stimulation MSWI fly ash and then studied that in real MSWI fly ash.Firstly, adding heavy metal chlorides to the mixture CaO and SiO2 as stimulation MSWI fly ash. The volatilization of Cu,Pb,Zn and Cd were characterized on basis of experimental evidence, the experiments were conducted in a atom-scale high temperature TG-DTA system. The Ca/Si, atmosphere, heating rate, that influence the volatilization rate and reaction characteristics, had been studied. The result showed that: along with the Ca/Si rising, TG and DTG curves of volatilization process moved to the high temperature direction, and comparing with no Ca/Si, the reaction temperature of the four heavy metals increased on certain degree but the volatilization ratios decreased.Secondly, with the TG data, this paper worked out the kinetic models of the volatilization of Cu,Zn and Cd with different Ca/Si, using the theories of inconstant temperature kinetic. The result showed that: not only the reaction active energy and pre-index factor were changed by Ca/Si, but also the volatilizatio reactions mechanism was changed.Thirdly, adding CaO and SiO2 to real MSWI fly ash to make different Ca/Si fly ash. The volatilization of Cu,Cd and Pb were characterized on basis of experimental evidence, the experiments were conducted in a tube oven. The temperature, Ca/Si, that influenced the volatilization characteristics, had been studied. The result showed that: adding CaO and SiO2 were both increased the volatilization of Cu and Pb, but the volatilization of Cd were decreased with the increasing of Ca/Si; the volatilization rate of Cu and Cd were influenced by Ca/Si, the volatilization rate of Pb was not influenced.Finally, this paper worked out the kinetic models of the volatilization of Cu,Cd and Pb with different Ca/Si, using the theories of constant temperature kinetic. The result showed that: not only the reaction active energy and pre-index factor were changed by CaO/SiO2, but also the volatilization reactions mechanism was changed. This had a good comparability with the experimental of stimulant MSWI fly ash.