AUTHOR=De Matteis C. , Mantovani L. , Tribaudino M. , Bernasconi A. , Destefanis E. , Caviglia C. , Toller S. , Dinelli E. , Funari V. 

TITLE=Sequential extraction procedure of municipal solid waste incineration (MSWI) bottom ash targeting grain size and the amorphous fraction

JOURNAL=Frontiers in Environmental Science

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2023.1254205

DOI=10.3389/fenvs.2023.1254205

ISSN=2296-665X

ABSTRACT=Introduction: Bottom Ashes (BA) constitute a significant by-product obtained during the incineration of Municipal Solid Waste in Waste to Energy (WtE) plants. The BA are an heterogenous material made by different fractions, glass, minerals, metals, and unburned residual organic matter. Due to the nonhazardousness nature of the unburned material, BA can be effectively recycled becoming a valuable resource. However, BA display a high content of Potentially Toxic Elements (PTE) within its finer grain size. The presence of these elements raises concerns regarding the potential toxicity associated with BA.Materials and Methods: the release of PTE in the smaller fraction (0.063 -0.2mm; 0.3 -0.5mm; 2 -4mm; bulk < 4mm) of BA collected from the Parma WtE plant was investigated using a new five-step Sequential Extraction Procedure (SEP). Through this method, both leached solutions and solid residues were analyses by ICP-MS, XRPD and XRF. This integrated approach provided valuable insights into the mineralogy, chemical composition and PTE leachability of BA.Results and discussion: the novelty of this work is the development of a new SEP protocol, specifically designed and planned for an anthropogenic material such as BA. The weight reduction recorded after each step is linked to the progressive disappearance of both crystalline and amorphous phases. Water-soluble phases, such as salts, are the first to react followed by the carbonate fraction in the second step. At the end of the procedure, only quartz, corundum and Ti-oxide are identified. This is a provisional file, not the final typeset article Among the PTE, Pb exhibits the highest release, particularly during the acid-based attack, followed by Zn. The significant release of Ni during the oxidizing and reducing steps can potentially be linked to hydroxides and metallic alloy, respectively.The integration of XRF and Rietveld refinement results on solid residues enabled the identification of several types of amorphous materials and of their chemical evolution during the sequential extraction.