Study On Curing Performance Of Heavy Metals In Fly Ash From Municipal Solid Waste Incineration

Having the remarkable advantages of harmless, utilization and volume reduction, disposing of municipal solid wastes (MSW) by incineration has been widely used all over the world. However, MSW often mix with many substances containing heavy metals. During the course of incineration, the end product fly ash becomes the main carrier of heavy metals, which may damage the safety of ecological environment.According to the different identification standards for extraction toxicity of TCLP1311, HJ/T299-2007, HJ/T300-2007and HJ557-2009, one or more element of heavy metals exceed the limits in the 《Identification standards for hazardous wastes-Identification for extraction toxicity》(GB5085.3-2007), which means MSWI fly ash should be classified to the hazardous waste, and must be solidified or stabilized.The sequential extraction protocol for speciation analysis is an effective method to recognize their environment behavior of heavy metals. The transferring and transforming behavior of the heavy metals’ toxicity in MSWI fly ash depend on their speciation of element forms, which can provide scientific basis for the treatment and utilization for MSWI fly ash. Compared with other treatment methods for MSWI fly ash, the solidification by chemical agents has attracted more attention for its stable property in environmental factors.In this paper, the concentrations of heavy metals in MSWI fly ash, extraction toxicity and their speciation of elements by different identification standards were analyzed, and the solidification or stabilization properties for heavy metals in MSWI fly ash by using different heavy metal capturing agents were studied. The results provide a theoretical and technical support for disposing of MSWI fly ash.The distribution of different speciation of heavy metals in MSWI fly ash was studied according to the BCR sequential extraction protocol. The result shows that Cd and Cu in MSWI fly ash are mainly acid soluble, which would transform to the natural environment easily, and have strong biological toxicity. The proportion of reducible elements of As and Pb to their total concentration is30%-50%, which can be converted into acid soluble, and cause certain environmental risks. After solidification by using TBA, SGA, SDD and Na2S, the speciation of heavy metals are mainly changed to the more stable ones, the residual form increases while the acid soluble form was reduced. Compared with SDD and Na2S, TBA and SGA have an excellent comprehensive property in solidifying the heavy metals in MSWI fly ash. Take the dosage of1.0mol/kg as an example,97.27%acid soluble Cd, and91.18%acid soluble Cr are solidified after SGA’proposal, while100%acid soluble Pb changes to the more stable form after TBA’s solidification.