Sustainable exploitation of hidden resources: approaches for metal recovery and environmental remediation

Combustion residues, such as Fly (FA) and Bottom ash (BA), are produced during the incineration process in Municipal Solid Waste Incineration (MSWI) plants. Mine tailing (MT) is another industrial waste produced during the extraction of valuable resources from ores in mining operations. The present study considered these anthropogenic materials as alternative sources of strategic elemental resources. BA, FA, and MT samples are characterized by X-Ray Fluorescence (XRF) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for accurate determination of 49 elements, by applying both total and pseudo-total digestion. The analytical recovery of elements shows higher concentrations in BA than FA, especially industrial base metals, such as, Fe, Al, K, and Cu, and valuable elements (of strategic importance for the EU) like Co, Ba, and REEs. In time series analysis (2013-2022), FA material showed that Zn, Mg, P, Ti, and REEs like La, Ce, and PTEs (Pb, As, and Cd) are higher especially in Lime-doped FA (FAL) category than the Soda-doped FA (FAS) during the pre-pandemic period (2013 and 2020) than the post-pandemic period (2021 and 2022) for two MSWI plants waste considered. Pandemic-related changes throughout these years reflected the waste composition, in particular an increase in disposable materials and electronic waste burning. Gamma and Alpha Spectroscopy analysis explored the enrichment in radionuclides in FA and BA, identifying elevated activities for natural radionuclides (40K and 210Pb), which were almost constant during the years considered. In the characterization of four MT samples from active mines (Pb-Zn, Fe, Au, Cu), the pseudo-total digestion (aqua regia) showed the maximum leachable fraction of PTEs, encouraging the potential recovery considering MTs as a low-grade ore. The bibliometric analysis showed the research trends, suggesting that MSWI-ashes and MT can be subjected to sustainable treatment strategies for the circular economy.