Study On The Heavy Metals Distribution Characteristics In Msw Fly Ashes

In many countries incineration is taken to dispose municipal solid wastes for its advantage of over weight and volume reduction, detoxification and energy recovery. However, a coming second pollution problem attracts more and more attentions, such as persistent organic pollutants and heavy metals in flue gas and fly ashes. Fly ashes are the main residues of incineration, containing high concentration of heavy metals and persistent organic pollutants (PCDD/Fs, etc.). It's classified as hazardous waste in China, then should be treated harmlessly according to relevant standards.This paper, with fly ashes from incinerators and their heavy metals as the research object, summarized the hazards of heavy metals and harmless approach of fly ashes treatment, and analyzed the migration mechanism and influence factors of heavy metals during incineration. Then the fly ashes at different positions of two commercial operation incinerators-a fluidized bed incinerator (FBI) (550t/day) and a grate furnace incinerator (GFI) (350t/day) were sampled for laboratory research and analysis.In this paper, the basic physical and chemical characteristics of the fly ashes samples (three samples per incinerator) were studied:EDX was using for analyzing the element constitutes, Mastersizer and screen separation was using for analyzing the distribution of particle size, and ICPMS was using for analyzing content of the main heavy metals (Pb, Cd, Zn, As, Cu, Cr, Ni and Hg). The results showed that the particle size distribution was similar to normal distribution, and sizes of particles between 38μm and 150μm took 80% of mass percentage, the mass fraction of less than 38μm and larger than 106μm were very low; The Cl, S content of fly ashes of GFI were higher than FBI, Zn, Pb were the highest concentration heavy metals in the fly ashes, and the heavy metals concentrations in fly ashes of GFI were higher than FB.Subsequently, the fly ashes were separated by screen according to particle size, testing the heavy metals (Pb, Cd, Zn, As, Cu, Cr, Ni and Hg) content for analyzing influence of furnace, temperature, and particle size to the distribution characteristics. Of the volatile heavy metals, the original content was Zn>Pb>Cd>As, and in the different particle sizes of FBI fly ashes their contents differed little, but of GFI fly ashes, on the contrary; in the fly ashes of FBI, they mainly distributed in 38-56μm of FFA3,56-106μm of FFA2 and 56-75μm of FFA1. Of the hard-volatile heavy metals, the original content was Cu>Ni>Cr, basically higher in GFI than in FBI. Due to their characteristics, the contribution rate of the different particle size was similar to the mass distribution. When the temperature was over 400℃, the content of Hg was low in all the particle sizes, and the content of Hg in the fly ashes of baghouse had a closer relationship with its temperature.