Properties Of Municipal Solid Waste Incineration Fly Ash And The Stabilization By Sintering With Clay

Because of the remarkable advantages of less land occupied, stable operation, less time consumption, obvious reduction, complete innocuity and energy-recovery, disposal of municipal solid waste by incineration is widely used by developed cities worldwide in recent years. However, secondary pollutant fly ash is also generated after incineration, due to the high contents of heavy metals in fly ash, harmless treatment for fly ash is required.Taking MSWI(Municipal Solid Waste Incineration)fly ash in a refuse incineration power plant in Chongqing area as the research object, based on the researches on its physical and chemical properties, total contents of typical heavy metals, leaching toxicity and thermal properties, clay mineral montmorillonite and common clay are both respectively mixed with MSWI fly ash for sintering, and the impact of sintering temperature, sintering time and the two clay specimens on the stabilization of heavy metals are analyzed,the optimal sintering parameters for heavy metal stabilization are found.Experimental study shows that, among the total contents of heavy metals in MSWI fly ash, Zn is the element with maximum content, Pb takes second place, content of Hg is the minimum, leaching concentrations of Pb and Zn both far exceed identification standards of extraction toxicity, other heavy metals could all meet the requirements of the standards; sintering time and sintering temperature dramatically affect ignition loss of the major elements of Cl, K and the main toxic heavy metals Pb, Zn, Cu, Cd, Hg,Mn,Cr, etc. in MSWI fly ash.In the specimens of MSWI fly ash-montmorillonite and MSWI fly ash–common clay, the variation of heavy metals fixation rates with sintering temperature shows that, sintering temperature is an important factor impacting the fixation property of heavy metals in MSWI fly ash, which differ greatly with different sintering temperatures. In the temperature range of 800℃-1250℃, sintering temperature has a significant effect on the fixation fates of Pb, Zn and Cu, but not on those of Cr, Mn, Hg and Cd. Pb and Zn, the most abundant elements in fly ash, both reach their highest fixation rates(both higher than 80%) at the temperature of 1000℃-1050℃. The variation of heavy metals fixation rates with sintering time shows that,effect of sintering time on the heavy metals fixation rates in the two specimens is not obvious except Pb and Zn, and Pb and Zn, the main heavy metals in fly ash, both reach their best fixation rates at the sintering time of 1.0h. The comparison of the heavy metals fixation rates between the two clay materials indicates that, the fixation rates of various heavy metals in the two clay specimens are generally approximate, effect of clay minerals on the heavy metals fixation rates is not obvious. Comparatively, fixation rate of montmorillonite is generally higher than the common clay, so montmorillonite is a better clay material for heavy metal stabilization.After stabilization treatment by sintering at high temperatures, leaching concentrations of heavy metals in the two clay sintering products of MSWI fly ash-montmorillonite specimens and MSWI fly ash–common clay specimens are extraordinarily low, much lower than those of untreated MSWI fly ash specimen and the national identification standards for hazardous waste.While the sintering temperature is chosen 1000℃,sintering time 1.0h,montmorillonite as the clay material, the fixation effects of heavy metals are considerably good in MSWI fly ash-clay specimens,and the leaching concentrations of heavy metals are far lower than the identification standards for hazardous waste. Therefore, while MSWI fly ash is sintered with clay mineral, the heavy metals in MSWI fly ash could be effectively stabilized.