Chemical Changes of Municipal Solid Waste Incinerator Fly Ash under Short-Term Aging

摘要

The chemical composition of municipal solid waste incinerator (MSWI) residues can be changed by some parameters such as contacting with CO_2 and moisture. The leaching behavior of heavy metals from fly ashes is different according to the aging period and the exposure state. The effect of aging on the leaching behavior of heavy metals for the MSWI fly ashes was investigated in terms of open and closed condition. And also it was separately estimated in accordance with the kinds of fly ashes such as waste heat boiler (WHB) ash, semi-dry reactor (SDR) ash, and bag filter (BF) ash.Change of pH was clearly observed in the open sample of SDR ash although other samples have not significant changes of pH during 170 days. Moisture content of BF ash placed in open state has gradually increased until 50 days and then declined during the rest of aging periods. The fine particles of BF ash have turned into lump from 60 days in the open state. Pb and sulphate ion leaching concentrations have been reduced until 90 days for SDR and BF ashes in open state. Since 90 days Lead (Pb) concentrations of leachate have not changed any more, but Sulfate ion (SO_4~(2-) concentration from the open sample of SDR ash has increased during the rest of aging periods. In addition Magnesium (Mg) was detected in the leachate at this time and then the leaching concentration has gradually increased. Leaching ratio of Pb has not shown considerable changes in WHB ash. Change of Total Chromium (T-Cr) leaching concentration has been apparently shown in the open and closed sample of WHB ash. Leaching concentration of Cadmium (Cd) has gradually increased in the open sample of SDR ash since 40 days. Significant Changes for leaching concentration of Iron (Fe) and Copper (Cu) have not been observed in all samples. Since 30 days Potassium (K) and Sodium (Na) leaching concentrations have become almost same value in groups of the open and closed samples, respectively.