Properties and leaching characteristics of solidified waste forms for hazardous and radioactive incineration ashes

Abstract

Incineration has been known as an effective technology for the volume reduction and stabilization of combustible wastes into physically and chemically inert form. Incineration provides a high reduction of mass as well as volume. Consequently, thermal treatment of combustible wastes yields residues (termed ``incineration ash``) containing much higher toxicity than the original wastes. Moreover, the incineration ashes are highly dispersive and difficult to handle. It is highly recommended that the incineration ashes should be solidified to a form suitable for handling, transportation, interim storage, or final disposal. Based on the literature survey on the ash solidification technologies, studies on the solidification of hazardous waste incineration (HWI) ash and simulated radioactive waste incineration (RWI) ash was performed with an addition of three different kinds of binding matrices: hydraulic cement, cement/epoxy composite, or borosilicate base-glass. The physicochemical properties of the final waste forms were thoroughly investigated. For cement-based waste forms containing HWI ashes, the compressive strength and density ranged from 4~35 MPa and 1.26~1.89 g/㎤, respectively. Cement waste form showed a slightly higher value. The volume reduction factors for both waste forms were less than 1 indicating the increase of the final waste volume to be disposed of. The standard extraction tests showed that the HWI ash and its cement/epoxy waste forms should be categorized as hazardous (specific) waste since concentrations of some heavy metals in the extract exceeded the regulatory criteria, while those tests identified the cement waste form as a non-hazardous waste. Enhancement of the performance of the cement/epoxy waste form, which was expected by adding epoxy resin to the cement paste, could not be achieved. The glassy waste forms fabricated by melting the mixture of incineration ash and base-glass material at 1,300℃ had a density of over 2.60 g/㎥. The...