Temperature and pH Dependence of Some Metals Leaching from Fly Ash of Municipal Solid Waste

Abstract

Abstract. Municipal solid waste combustion leads to concentration of various metals in the solid residue (fly ash) remaining after combustion. These metals pose serious environmental hazard and require proper handling and monitoring in order to control their harmful effects. Leachability of some metals from fly ash was examined in fly ash and Milli‐Q water mixture (liquid‐to‐solid ratio, 100) under various temperature and pH conditions in the laboratory. The leaching experiments conducted for 24 hours showed that pH was generally more important than temperature in controlling the amount of metals leached out of the fly ash. However, at a given pH, rise in temperature led to different degree of (usually one to two fold) enhanced or reduced leaching of metals. Owing to amphoteric nature of oxides of Al, Cr, Pb and Zn, these metals often yielded typical pattern of increase and decrease in their concentrations with change in pH. The extent of leaching of Cr and Pb in our experiments suggests that decrease of pH to acidic range in the case of Pb and to neutral to acidic range for Cr over a long period of storage of fly ash at solid waste dumping site may facilitate leaching of these metals from fly ash, leading to contamination of groundwater to the level that exceeds beyond the level permitted by the environmental laws.

Heavy metal characterization of circulating fluidized bed derived biomass ash

“…Ash from biomass combustion may be used as construction materials [1] or fertilizers [2][3][4][5]. Nevertheless, some hazardous matters, such as heavy metals [6,7] and dioxins [8], may exist within the ash. Consequently, ash has to be environmentally friendly before use.…”

Chemistry of fly ash and cyclone ash leachate from waste materials and effects of ash leachates on bacterial growth, nitrogen-transformation activity, and metal accumulation

“…Fly ash produced by the combustion of coal is beneficial when used as a soil amendment to improve physical properties (such as soil water-holding capacity [2,3]); to improve chemical properties by increasing cation exchange capacity (CEC) [4]; to provide essential elements such as Si, P, K, and B to plants; to adjust soil pH to levels more suitable for agriculture [5]. On the other hand, many toxic substances such as heavy metals [6,7] and dioxins [8] are known to leach from incinerator waste ash. As a result, few studies have been performed examining the utilization of waste ash as a soil amendment.…”

Impact of Changes in Redox Conditions on Leaching of Some Elements from MSW Fly Ash

“…Each fly ash sample was acidified in triplicate with 1N HCl to remove carbonate carbon, dried on hot plate and analyzed for organic carbon content (Table 1). Further details on these analytical procedures have been provided in Gupta et al (2005).…”

“…Solid wastes, e.g. fly ash generated from municipal solid waste (MSW) combustion, are especially enriched in many toxic elements (Sawhney and Frink, 1991;Gupta et al, 2005). The mobilization of elements from waste is restricted for a long period of time due to presence of buffering substances in the waste.…”

“…Oxidation of OM results in net release of carbon dioxide, which forces pH to decrease in a system not in equilibrium with atmosphere (Förstner, 1995). Decrease in pH considerably enhances leaching of elements from fly ash (Gupta et al, 2005). Leachate is generated by excess rainwater percolating through a waste disposal site.…”