Leaching Characteristics Of The Fly Ash From Municipal Solid Waste Incinerator In Different Extracting Conditions

Municipal solid waste fly ash, the hazardous waste regulated by Chinese Law, must be disposed in security landfill. With application of incineration technique for municipal life refuse more and more often, fly ash increases swiftly and violently. However the capacity of security landfill is not enough, a large amount of fly ash was scattered into soil without any supervision and then underwater were polluted by it, which caused great environmental risk of pollution. Studying the leaching characteristic of pollutant from fly ash in different leaching condition, we provide theory for security treatment and disposal so as to decrease environment risk by fly ash.Effects of a water-extraction process on leaching characteristics of fly ash was studied using batch leaching experiment. The washing process had some effect on Cl, Na, K,and Ca leachabiliy reduction, and the leaching rate of Cl was almost 60% at L/S (liquid to solid ) =10. The leaching concentration of heavy metal of leachate decreased with L/S increase. There were no characteristic peaks for NaCl and KCl in evidence by X-ray diffraction (XRD) after water extraction, and there was little change in characteristic peaks of quartz and gypsum. KCl and NaCl was the major leaching form of K, Na and Cl in the washing process. The washing process had less effect on acid neutralization capacity. Leaching concentration of heavy metal from washed fly ash was higher than that from raw fly ash in TCLP testing and horizontal vibration methods.A column-like experiment was used to simulate the leaching process of fly ash in practice disposal, and to study the characteristic of fly ash in flow-through system. With the flow of water in flow-through system, the concemtration of major element Ca leapped and transfered, and the transfer of front happened at the same time with the front of pH. After column-like test major element Na, K and Cl of fly ash were almost washed out, Cl which was 14.6% in raw fly ash decreased to 0.6% in each cell, which decrease 14.0%; K and Na which were 7.9% and 6.4% respective decresed to 3.3% and 1.2% in each cell, which decreased 4.6% and 5.2% respective. Heavy metal of fly ash cumulated lightly at the front, and leaching concemtration of leached fly ash was lower than raw fly ash in TCLP. Effect of time scale on leaching was important for the leaching in flow system.In conclusion, the differences of leaching characteristic in different leaching condition was confirmed through studying leaching behavior of fly ash in water-extraction process and flow-through system. The result can provide data support for leaching behavior of fly ash from our country's municipal solid waste and environmental risk appraisal in disposal and treatment.