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Global Journal of Environmental Science and Technology 2012, 2: 7
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Review Article
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Management of hazardous fly ash: A review
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A. T. Lima
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Department of Earth Sciences, Geochemistry, Faculty of Geosciences, Utrecht University,
PO Box 80.021, 3508 TA Utrecht, The Netherlands
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Abstract |
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An integrated waste management presents a hierarchy of management activities, established by a series of regulations, with the purpose of decreasing the disposed waste in landfill. Incineration, a waste transformation technology, is growing as a solution, not only for waste volume reduction, but also as a heat recovery technology. The use of combustion systems is a current option for low CO2 production of electric power. Fly ash is one of the byproducts of such a process, considered a hazardous waste. Several reuses are proposed for such a waste, once the hazardous compounds have been removed. Fly ashes are then one of the waste products from incineration of coal, urban or industrial residues and biomass to mention a few. Fly ash is the general term used for incineration byproducts, namely particulates and flue gas additives captured from the flue gas stream. They are considered hazardous due to their content on contaminants, especially heavy metals. Fly ashes constitute an environmental problem both due to their hazardousness and instability, needing previous stabilization before disposal in landfill. The landfilling of such hazardous material has been described by several authors, where some refer special ash landfills, others industrial waste landfills, some wet disposal, others dry disposal. Besides the hazardousness, fly ashes also possess features that could de further valorized in uses as different as soil amendment, ceramics or concrete. For instances, fly ashes from the combustion of coal are frequently used as adjuvant for obtaining high performance concrete. However, due to contaminant enrichment of fly ash fraction, the reuse of such a waste should be always in accordance with the precautionary principle and the uncertainty of the contaminants behavior throughout time. The present review is dedicated to the characterization of different fly ashes, its handling and the minimization of heavy metals leachability to the surrounding environment. Fly ashes from municipal solid waste (MSW) incineration (with and without lime addition), fly ash from straw (ST) combustion, and fly ash from co-combustion of wood with fuel oil and natural gas (CW) are here under discussion. The approaches vary on a specific point: (i) remediation, where the contaminants are extracted from the solid porous fly ash, (ii) stabilization/solidification (S/S), where contaminants are embedded in a solid matrix. In order to understand the origin of fly ashes and its formation, a review on the incineration process and its efficiency is given. According to literature, fly ashes are dependent of incineration parameters such as temperature, and, most importantly, the fuel/waste. Furthermore, fly ash is defined, the electrodialytic process for its remediation is described and a possible reuse is assessed, always considering the precautionary principle.
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Keywords |
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Fly ash; Waste management; Remediation; Electrodialytic process; Heavy metals
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