Particle Size Distribution and Speciation Analysis of Heavy Metals in Municipal Solid Waste Incineration Fly Ash in Chongqing, China

The distribution in different particle size of municipal solid waste incinerator fly ash were studied by sieve method, and the heavy metal content and speciation of Pb, Cd, Zn, Cu, Mn, Ni and Cr in different particles were analyzed by Tessier's sequential chemical extraction procedure. The results showed that more than 90% of fly ash's particle size was less than 250 μm, while particles of 150~250 μm accounted for about 50%. Content of heavy metals were decreased first and then increased with decreasing particle sizes except Ni. Concentration of heavy metals in fractions of <;250 μm takes up 90% of the total. With the changing of the fractions of fly ash particles, the content of speciation varies from different types of heavy metals. It was also found that the elements such as Zn, Cd, Pb and Cu have exhibited a remarkable content in the form of exchangeable cations. They would be released into the environment under acid rains especially in Chongqing, which would result in a potential risk to the environment.

Introduction

Incineration is considered to be one of the effective treatment approaches for municipal solid waste (MSW) for its simultaneous energy recovery and pollution minimization. Municipal solid waste incineration (MSWI) has attracted increasing attentions recently in China due to site unavailability for landfill as well as rapidly increasing land price. Although the removal efficiency is good when use incineration method to treat the combustible waste, there would generate the fly ash in the process and the amount is 3%~5% of the total amount of waste^[1]The waste fly ash, which enriched many heavy metals and a little of organic pollutants, such as dioxins and furans, which has been classified as hazardous waste in the environmental regulations in China and it must be treated with the safe landfill method^[2]. The toxicity of heavy metal in fly ash is not only related to the total amount of heavy metal, but the speciation distribution of it in a greater degree. The difference of biological and environmental effect of each heavy metal is great in spite of the total amount is same^[3].