Assessment of Fossil Fuel Fly Ash Formulations in the Immobilization of Hazardous Wastes.

In this work, a simple and inexpensive method is introduced for the immobilization of the hazardous elements Cd, Pb, and Fe from their aqueous solutions in compressed fossil fuel fly ash formulations, as candidates for waste forms. The molded formulations were prepared by initially mixing the hazardous waste solutions with the fossil fuel fly ash material at a constant ratio (17%). Then the resulting pastes were pressed at the appropriate pressure using a manual hydraulic press. The compressed formulations revealed good water resistance, compression strength, and radiation resistance. Leachability investigations of the molded matrices were performed in terms of the accelerated leach test, the toxicity characteristic leaching procedure (TCLP), and long-term leach tests. The TCLP results obtained for Cd and Pb were well below their TCLP limits. On the other hand, the accelerated and long-term leach tests showed a similar behavior. The properties of the compressed formulations revealed their high performance as an alternative for waste forms as indicated by their durability, compression strength, and leachability. The low leachability of Cd, Pb, and Fe from the compressed fly ash formulations could be attributed to a dual mechanism of microencapsulation and/or chemical fixation. [ABSTRACT FROM AUTHOR]

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