Potentially toxic elements in bottom ash from hazardous waste incinerators: an integrated approach to assess the potential release in relation to solid-phase characteristics

Understanding the chemical and mineralogical characteristics of bottom ash (BA) containing Potentially Toxic Elements (PTEs, e.g., As, Cd, Co, Cu, Cr, Mo, Ni, Pb and Zn) is necessary because it provides information to the potential environmental impacts and possible management options. In this study, we used an integrated approach, combining solid phase characterization [by X-ray diffraction (XRD) and Field Emission Gun Electron Probe Micro Analysis (FEG-EPMA)] and leaching tests. XRD analysis for mineralogical characterization was used but turned out not always to allow detecting discrete mineral phases containing PTEs. Therefore, FEG-EPMA, which is less often used for waste characterization, was used to provide information on the elemental associations focusing on some PTE retaining phases. This allowed direct solid phase characterization and investigation of the relationship between discrete and bulk solid-phase characteristics and PTE leaching behavior from BA. Some environmental scenarios related to PTE release were also assessed. Liming can reduce the PTE concentrations in the leachates to a desirable level, but the release of Mo from one of the BA samples would still be of concern. Our results indicated that attention should be paid to the safe disposal of this BA to avoid leaching of Mo and contamination to environment.