Proceedings of the 41st Congress on Science and Technology of Thailand (STT41)
Congress on Science and Technology of Thailand (STT41) edition:41 location:Nakhon Ratchasima (Thailand) date:6-8 November 2015
Incineration is a common technique for waste treatment because it can reduce waste mass and volume. However, the residue (bottom ash) may contain a considerable amount of Potentially Toxic Elements (PTEs, e.g., As, Cd, Co, Cr, Cu, Ni, Mo and Zn). In the present study, besides the investigation of the bulk chemical composition, the cascade leaching test was used to assess the release of PTEs from bottom ash samples collected from hazardous waste incinerators in Ho Chi Minh City (southern Vietnam). Results from the leaching test indicated that the leachability varied among the PTEs. Molybdenum exhibits the highest leachability (8 – 11 %) whereas most of the other PTEs including Co, Cr, Cu, Ni, Pb and Zn exhibit a low leachability (< 1 %) in both samples. Similar release patterns of Fe, Co and Ni were observed in one of the samples. This suggests that they might originate from the same host phase or that they are retained by similar binding mechanisms in this bottom ash sample. Solid-phase characterization also supports this hypothesis.
Mineral identification by X-ray diffraction revealed the presence of magnetite (Fe3O4) and hematite (Fe2O3) while Field Emission Gun Electron Probe Micro Analysis showed the co-existence of Co and Ni in Fe-alloy and Fe-oxide phases in this sample. Despite the fact that water acidified to pH 4 was used in each step of the leaching test, the pH of the leachates varied from neutral to slightly alkaline values. This might delay and prevent the release of the PTEs from the studied samples. Moreover, the low release of some PTEs (except Mo) in these conditions can be explained by the PTE associations with Fe-bearing phases which are usually found in combustion residues. Results from this work suggest that special attention should be paid to the safe disposal of these bottom ashes to avoid leaching of Mo and contamination of the surrounding environment.