title: Evaluation of heavy metal leaching from coal ash-versus conventional concrete monoliths and debris.
abstract: Application of coal ash in construction materials is constrained by the potential risk of heavy metal leaching. Limited information is available on the comparative heavy metal leaching from coal ash-versus conventional concrete. The current study compared total and leached heavy metal concentrations in unbound coal ash, cement and sand; and investigated the effect of initial leachant pH on heavy metal leaching from coal-ash versus conventional concrete monoliths and their debris. Total Pb, Mn and Zn in coal ash were lower than or similar to that of other materials, while Cu and Fe showed the opposite trend. Leached concentrations of Zn, Pb, Mn, Cu and Fe in unbound coal ash, its concrete and debris were comparable and in some cases even lower than that for conventional concrete. In all cases, leached concentrations accounted for just <1% of the total concentrations. Log-log plots of concentration and cumulative release of Fe versus time based on tank leaching data showed that leaching was dominated by diffusion. Overall, the risk of Zn, Pb, Mn, Cu and Fe leaching from coal ash and its concrete was minimal and comparable to that of conventional concrete, a finding in contrast to widely held public perceptions and earlier results reported in other regions such as India. In the current study the coal ash, and its concrete and debris had highly alkaline pH indicative of high acid neutralizing and pH buffering capacity, which account for the stabilization of Zn, Pb, Mn, Cu and Fe. Based on the low risk of Zn, Pb, Mn, Cu and Fe leaching from the coal ash imply that such coal ash can be incorporated in construction materials such as concrete without adverse impacts on public and environmental health from these constituents.
authors.affiliation: Biosystems and Environmental Engineering Research Group, Department of Soil Science and Agricultural Engineering, University of Zimbabwe, P.O. Box MP167, Mt. Pleasant, Harare, Zimbabwe. Electronic address: wgwenzi@yahoo.co.uk.
authors.forename: Willis
authors.initials: W
authors.lastname: Gwenzi
authors.affiliation: Biosystems and Environmental Engineering Research Group, Department of Soil Science and Agricultural Engineering, University of Zimbabwe, P.O. Box MP167, Mt. Pleasant, Harare, Zimbabwe.
authors.forename: Nyarai M
authors.initials: NM
authors.lastname: Mupatsi
mesh_terms: D060729:Coal Ash / Q000737:chemistry*; D003252:Construction Materials / Q000032:analysis; D004553:Electric Conductivity; D004785:Environmental Pollutants / Q000032:analysis / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D019216:Metals, Heavy / Q000032:analysis / Q000737:chemistry*; D015030:Zimbabwe
chemical_list: D060729:Coal Ash; D004785:Environmental Pollutants; D019216:Metals, Heavy
keywords: Alkaline pH; Batch; Coal ash; Conventional concrete; Debris; Semi-dynamic leaching