[Characterization and heavy metals leaching toxicity of fly ash from municipal solid waste incinerators in China]

The characteristics and leaching behavior of heavy metals in fly ash, sampled from 12 MSWI plants in China, were investigated. The results indicated that the main elements of fly ash were Si, Ca, Al, Fe, K, Na, Cl, and the total fraction of heavy metals was in the range of 0.5 % - 3.0% with the exception of one sample. Therefore MSWI fly ash must be controlled as hazardous materials because of its potential environmental risk. The leaching ratios of heavy metals in fly ash were low to some extent according to the results of batch tests such as Toxicity Characteristic Leaching Procedure (TCLP) of U. S. EPA and GB 5086.1-1997. The notable variance of TCLP and GB 5086 evaluating the same sample was due to the obvious difference of pH values in leachate. The result of general acidity neutralization capacity (GANC) showed that the leaching behavior of heavy metals in fly ash were controlled by the final pH of leachate, which was determined by the inter-reaction of alkaline in fly ash and acidity of leachant. The end points of equilibrium in batch test and flow-through test had great difference based on the analysis of these procedures. It is of significant meaning to build a batch procedure basing on the disposal scenarios and characteristics of fly ash for the purpose of adequate risk assessment and management.