Research On Leaching Properties And Stabilization Of Municipal Solid Wastes Incineration (MSWI) Fly Ash

The management of solid wastes is one of the most difficult environment problems at present, and the application of MSWI is become more and more popular. MSWI fly ash contains many heavy metals and dioxins, so it is regarded as hazardous waste and need be stabilized before disposal.The leaching properties of MSWI fly ash at different pH values are studied. The effect and leaching properties of immobilization of cement are investigated. The melting temperature is reduced by fly ash with some additives, the leaching properties of original glass at different pH values are studied. The best nucleation and crystallization temperatures are determined by DTA, and glass-ceramic have been made from original glasses after the melting process, the microstructure characteristics and crystallized phase of glass-ceramics have been investigated by SEM and XRD. at the same time, the fly ash is washed by water, removing the Cl contained, which can reduce the produce of chloride of low melting point and increase the rate of melting and glass solidification of heavy metals.The results show: the leaching toxicity of Cr,Zn,Pb,Cu and Cd in fly ash decreases with the increases of the pH of leachate, the leaching toxicity of heavy metals greatly increases under acidity conditions, and the leaching toxicity under pH=3 condition is the strongest in this experiment, the leaching toxicity of Cr,Pb,Cd is higher than the standard, but in alkaline environments, part of heavy metals have leaching phenomenon. The immobilization of cement on MSWI fly ash is effectual, but in acid environment, the heavy metals in cement solidification body remove to the environment as time flies, which lead to no effect. The melting and glass solidification body includes steel slag,soda ash,borax can reduce the melting temperature to1200℃, it conclude 72% fly ash. The original glass has little leaching concentration at different pH values, especially under pH=2 condition. So this original glass has no leaching toxicity and can be used safely. The best nucleation temperature is 650℃and crystallization temperature is 900℃, nucleation and crystallization times both are 2h. Its major crystallized phase is diopside(Ca(Mg, Fe, Al)(Si, Al)2O6). Through the pretreatment process of washing by water, the remove efficiencies of Cl, Na, and K are above 50% respectively, and the remove efficiency of Cl reaches 98%. At the same time, the solidification effects of heavy metals increase greatly, and the increasing values for different metals are arranged as the following: Pb>Cu>Cr>Zn>Cd. In a conclusion, it is an effective pretreatment process for fly ash to wash by water, which controls the secondary environmental pollution because of increasing of solidification effects, and decreasing of volatilization of heavy metals in melting process.The results show that the immobilization of cement and the melting and glass solidification on fly ash have little leaching concentration, what's more, the melting and glass solidification body is more steady and safety. The melting temperature is reduced and change the original glass into glass-ceramics can reduced the cost, it is an effective pretreatment process for fly ash to wash by water, which controls the secondary environmental pollution because of increasing of solidification effects, and decreasing of volatilization of heavy metals in melting process.