Research On Stabilization Of Heavy Metals In MSWI Fly Ash Through Segmented Hydrothermal Treatment

Due to the process is simple and reliable, incineration technology gradually become one of the main methods of treatment of municipal solid waste in china. However,the fly ash produced by incineration contains high concentrations of heavy metals and dioxin and other pollutants have been recognized hazardous waste requiring further treatment. The synthesis of zeolite-like materials from municipal solid waste incineration(MSWI) flyash by a hydrothermal treatment is environmentally safe and technically possible. However, the residual liquid that is produced during the synthesis contains high concentrations of heavy metals(lead, zinc, etc) need to be treated prior to discharge. An alkali solution pretreatment process was added to improve the hydrothermal technology.1.Solid waste-Extraction procedure for leaching toxicity-Acetic acid buffer solution method(HJ/T 300-2007), Solid waste-Extraction procedure for leaching toxicity-Sulphuric acid & nitric acid method(HJ/T 299-2007), Solid waste-Extraction procedure for leaching toxicity-Horizontal vibration method(HJ 557-2010) and toxicity characteristic leaching procedure(EPA1311) were used to investigate heavy metal leaching from MSWI fly ash. Pb and Zn were leached out during HJ/T 300 method more than that during TCLP method,and during HJ/T299 method were leached out the least.2. Fly ash was treated by the hydrothermal processing under different conditions. The results show that : fly ash under certain conditions of NaOH concentration and reaction temperature synthesised such as Katoite, Tobermorite and Sodalite and other types of zeolite-like minerals, while the synthetic products leaching toxic reduced. However,excess NaOH or excessively high temperature will lead to Zn and Pb stablilization efficiency declined. The result show that reaction temperature 120℃ and 1mol/L NaOH is more reasonable.3. Alkali soluble preprocessing steps improved stability of heavy metals in MSWI fly ash through hydrothermal treatment. Discusses the leaching of lead and zinc soluble of alkali pretreatment process, the optimal conditions for reaction temperature is 70 ℃, reaction time is 50 minutes, and alkali concentration is 4 mol/L. The result of leaching toxicity analysis show that the segmented hydrothermal treatment can stabilize heavy metals in waste incineration fly ash more effectively, and reduce secondary pollution of the synthetic product and the residual liquid.