Heavy Metal Solidification Experimental Study Of MSWI Fly Ash

In recent years,Municipal solid waste incineration has been applied widely in China because it has obvious advantages, such as harmless, utilization, volume reduction.However,the MSWI fly ash is considered as hazardous solid waste according to the country policy, because it contains heavy metals which may damage the safety of ecological environment.The MSWI fly ash must be solidified and stabilized before entering the domestic waste landfill.According to the identification standard for extraction toxicity of HJ557-2010,more then one element of heavy metals beyond the limits of the GB 5085.3-2007,and it means that the MSWI fly ash belong to hazardous solid waste. According to the identification standard for extraction toxicity of HJ/T 300-2007,more then one element of heavy metals beyond the limits of the 《Standard for Pollution Control on the Landfill Site of Municipal Solid Waste》(GB16889- 2008),which means the MSWI fly ash should be solidified and stabilized before landfilling.In this paper, chemical composition,micro appearance,crystals, concentrations of heavy metals, extraction toxicity by different identification standard, and BCR chemical speciation of three kinds of MSWI fly ash have been analyzed.The solidification properties of heavy metals and their transformation in MSWI fly ash by using three chelating agent were studied.Three-step sequential chemical extraction method established by Reference Material Office of former European Community was used to study chemical speciation of seven heavy metals(Cr,Ni,Cu,Zn,As,Cd,Pb) in MSWI fly ash.The results showed that Cd existed in weak acid soluble form accounted for 35%~45% in WH1 and WH2 fly ash.The proportion of reducible Pb,Cu,Zn is higher than 30%,and this part may transform to acid soluble form in certain circumstances. The obtained results indicate that the speciation metals of the heavy metals became more stable after solidification with Na2S、SDD andTMT60.SDD and TMT60 are more effective in solidifying the heavy metals in the free kinds of MSWI fly ashes.For example, adding 6% dosage of TMT60,the proportion of reducible Cu,Pb in CZ fly ash are reduced from 74.08%,40.94% to 2.19%,18.27%; The proportion of acid soluble Cd in WH1 fly ash is reduced from 38.78% to 0.32%,and the reducible Cd is reduced from 48.54% to 13.79%; The proportion of acid soluble Cu in WH1 fly ash are reduced from 11.33% to 0.01%,and the reducible Cu is reduced from 39.67% to0.01%; The proportion of reducible Pb in WH1 fly ash is reduced from 32.49% to 2.70%.