Leaching of calcium and heavy metals from fly ash by acetic acid and life cycle assessment of the leaching processes

Abstract

Municipal solid waste incineration (MSWI) fly ash poses severe environmental risks because of the high potential of fly ash for heavy metal leaching. In this study, the leaching of fly ash by acetic acid was investigated. Key parameters, including time, acetic acid concentration, and fly ash type, were examined for their influence on calcium and heavy metal leaching. The physical and chemical changes in fly ash before and after leaching were analysed via the X-ray fluorescence (XRF), X-ray diffraction (XRD), and heavy metal leaching methods. The results showed that acetic acid effectively leached metals from different types of fly ash, as determined by the risk assessment code (RAC) and risk index (RI), and leaching with 0.25 mol/L acetic acid resulted in the lowest environmental hazard for fly ash. Moreover, adjusting the pH to below 11 during acid treatment, followed by washing with water, substantially reduced heavy metal leaching and increased the potential for safe resource recovery. A life cycle assessment (LCA) using the CML-2001 method revealed that the marine aquatic ecotoxicity potential had the largest environmental impact, accounting for 39.56% of the total index. These findings suggest that acetic acid leaching followed by water washing, improves the potential for repurposing of fly ash as a construction material.

Graphical abstract