Incinerator ash characterization – Implications for elevated temperature landfills

The occurrence of temperatures in municipal solid waste (MSW) landfills in excess of 55 °C is a problem that has gained much attention in the solid waste industry, both domestically and globally. Facilities which frequently experience such temperatures are termed Elevated Temperature Landfills (ETLFs). Ash, both MSW incinerator ash (MSWIA) and coal combustion ash (CCA), when co-disposed with unburned MSW, can provide constituents which are able to partake in abiotic exothermic reactions that may develop or sustain elevated temperatures. These reactions include hydration and carbonation, as well as the oxidation and corrosion of metals commonly found in ash. In this study, sixteen ash samples from across the U.S. were characterized by using X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy coupled with X-ray energy dispersive spectroscopy (SEM/XEDS) to identify complex mineral and glassy phases enriched in calcium, silicon, aluminum, and iron. The high-temperature incineration of MSW and coal feedstocks, along with weathering processes impacting these ashes, yield a heterogenous material capable of generating appreciable heat given the right conditions. Additionally, a simple model was developed and, using ash compositions obtained via XEDS, a value termed relative heat potential (RHP) was estimated for each sample. Results show that CCAs may be expected to generate roughly 15 % more heat than MSWIAs when deposited in landfills due to their greater aluminum content.