Study on physiochemical properties and leaching behavior of residual ash fractions from a municipal solid waste incinerator (MSWI) plant

Abstract

Generally, Fly ashes (FAs) in Municipal Solid Waste Incinerator (MSWI) are classified as hazardous waste and commonly managed in a mixed way even though distinct FA in incineration flows have different characteristics. Thus, it can cause improper management of fly ashes and an increase in cost as well as the volume of residual ashes sent to the hazardous landfill. In this study, Bottom ash (BA), Secondary furnace ash (SFA), Superheater ash (SHA), Boiler chamber ash (BCA), Economizer ash (EA), and Baghouse Filter Ash (BHFA) have been sampled separately from different locations at an MSWI plant. An integrated approach involving physical, chemical, mineralogy, and leaching behavior was used to characterize the residual ashes. Results point out that the average diameter of ash particles varies from 4.87 μm for BHFA to 6825 μm for BA, with three distinct zones. The Blaine fineness value increases when the median size of ash particles decreases. All values of Loss on Ignition (LOI) at 550 °C are less than 3%, indicating a suitable burning. The main mineralogical crystalline phases in ashes were KCl, NaCl, Mg.6Al1.2Si1.8O6, CaCO3, CaSO4, CaSO3, and SiO2. Among the considered heavy metals, leaching tests identified high levels of hazardous waste for Pb, Cd, Cu, and Zn in BHFA as well as for Pb and Zn in SHA. BA, SFA, BCA, and EA are categorized as non-hazardous according to the TCLP (USEPA-1311). In terms of EN 12457-2 test, BA and SFA are inert waste; but SHA, BCA, and EA are classified as hazardous waste due to a significant level of Cl. The results show that the characteristics of ash in the separate location of the MSWI process is essential to have an economical and proper solution for ash management.