RELEASE OF METALS FROM MSW-I FLY-ASH AND AVAILABILITY IN ALKALI CONDITION

The release and availability of Pb, Cd, Cu, Zn from municipal solid wa ste (MSW) fly ash were studied with an emphasis on its behavior under alkaline conditions. Serial batch tests using acidic and alkaline solu tions as leachant and a pH stat test were carried out. From the result s of serial batch test: (1) Even if the ash comes into contact with st rong acid for a long period, pH of the leachates from some fly ashes a re high, and the concentration of Pb in the leachate is high. (2) When the ash comes into contact with the alkaline leachant, even if the Ay ash has little alkalinity, the pH of the leachate soon increases and the concentration of the Pb and Zn in it are high. (3) The fact that l eaching of heavy metals from fly ash depends on the pH of the leachate was certificated. From the pH stat test: (1) The larger the liquid pe r solid ratio (L/S), the more metals are released. (2) Leaching behavi or of Pb is different from other metals and leached in high concentrat ion in alkali condition. (3) Concentration of metals in leachate is co ntrolled not only by solubility but other factors and were certificate d. Moreover, considering the properties of the ashes, the optional pro cedure of the availability test for Pb was proposed. (C) 1997 Elsevier Science Ltd.