MINERALOGY AND SURFACE-PROPERTIES OF MUNICIPAL SOLID-WASTE ASH

Bulk chemical analysis shows most elements enriched over average soil abundances except for Si, which is 60% of the concentration in soils. Eleven minerals were identified using powder X-ray diffraction (XRD). Standard additions using XRD gave the following weight percent of minerals (+/-2sigma) in combined bottom and fly ash: gypsum, 1.8 +/- 1.9; hematite, 3.7 +/- 1.7; quartz, 2.3 +/- 1.0; spinel, approximately 3.5; halite, 0.5 +/- 0.4; calcite 3.5 +/- 1.9; rutile, 1.1 +/- 1.3. Mullite, sylvite, anhydrite, and wustite were also identified. The ash contains 18% minerals. 9% structural and adsorbed water, and 72% glass. An estimated composite glass composition is reported. Chemical sequential extraction showed that most Cr is present in phases resistant to chemical weathering, while significant Cd and Pb are sequestered in acid-soluble (carbonate) phases. Little of these toxic trace metals are water soluble or in exchangeable surface sites. The ash has a pH-dependent cation exchange capacity of 25-55 mequiv/100 g, suggesting surface sites are available to sequester metals.