Long-term assessment for the leachate release of heavy metals from municipal solid waste incineration bottom ash monofills

Municipal solid waste incineration (MSWI) bottom ash was investigated by ch emical, mineralogical, and microbiological methods as well as leaching- and laboratory lysimeter tests. Compared to geological material bottom ash sho ws a high content of soluble salts, organic carbon, and heavy metals. The h eavy metals are mainly bound in alloys and glas. Addition of oxic and aceti c solutions quickly oxigenize the metal-phases and alloys. Only fixation in newly formed phases like carbonates or hydroxides prevents heavy metal rel ease till pH 7 in case of pH-reduce. In the long-term the acid buffer is re duced by the environmental acid input in combination with the release of bu ffering phases (mostly calcite). Internal acid producing processes like dec ay of organic matter or oxidation of sulfides are not important for the pH- decrease. Cu, Ni, and Zn are first released between pH 7 and 6 (mainly Zn) and a second time at pH values below 5 (mainly Cu). Pb is significantly rel eased at pH values below 5, Cr only at pH < 4. Mainly metals, alloys, and t he rims of glas are destroyed by leaching. Phases like metal hydroxides (ma inly Fe-phases) or amorphous, water bearing Fe-Al-Si-oxides are finally for med. Long-term leaching by acetic fluids increases the total availability o f heavy metals (except Cr) with increasing time. Kinetic effects including changing of metal binding forms seem to be responsible for this development . Within deposit conditions of limited gas exchange (closed system) the pH of the carbonate buffering zone can drop below pH 7 in case of very strong acid input and quickly cause an enhanced metal release. But in reality such a strong acid input is not to be expected. Calcite will buffer between pH 8 and 7 for a long time. Depending on the environmental conditions (water b alance, acidity of rain) and landfill design (compaction, permeability, cov er, thickness) it can take hundreds till thousands of years until metal rel ease will start. The long-term metal release of matter with an acid buffer like carbonates call be approximately determined only by short-term tests w ith powder (e.g. pH(static) tests at pH 4).