Secondary mineral formation in coal combustion byproduct disposal facilities: implications for trace element sequestration
Rona J. Donahoe, 2004. "Secondary mineral formation in coal combustion byproduct disposal facilities: implications for trace element sequestration", Energy, Waste and the Environment: a Geochemical Perspective, R. Gieré, P. Stille
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Coal combustion byproducts (CCBs) are high-volume wastes produced by the electrical power industry and typically disposed of in landfills and lagoon impoundments. In the disposal environment, meteoric water or groundwater may percolate through and interact with the ash materials, producing leachate that contains elevated levels of many trace elements. Various geochemical reactions control the release of solutes and the formation of secondary minerals in CCB disposal facilities during weathering. Concern about the potential release of trace elements into the environment has motivated a large number of studies aimed at predicting the maximum concentrations of elements in leachate solutions. Secondary minerals formed during weathering of CCBs have the potential to limit the mobility of trace elements in an ash disposal facility. Geochemical modelling has been used by many investigators to predict the equilibrium concentrations of solutes in CCB leachate solutions and the stable secondary minerals that will form in weathered ash. Unfortunately, basic kinetic, thermodynamic and adsorption data are lacking for many solid phases, particularly those that may contain trace elements. In addition, secondary solid phases are very difficult to identify by direct analytical methods due to their low abundances and/or amorphous character, so it is often not possible to directly determine the identity and compositions of secondary phases in ash disposal environments. Despite these difficulties, numerous secondary solid phases have been directly observed and/or predicted to form via weathering reactions in CCBs. A tabulation of all secondary phases that have formed or have the potential to form in the CCB disposal environment is given, along with the relevant references. The potential for secondary phases to sequester trace elements via precipitation, adsorption and co-precipitation is discussed. Secondary phases with the greatest potential to limit the mobility of trace elements are amorphous Fe-oxyhydroxide and amorphous aluminosilicate phases, which are metastable precursors to Fe-oxide and clay minerals, respectively.
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This book provides incentives for further development of sustainable fuel cycles through a novel and interdisciplinary approach to an Earth science-related topic. The main focus is on geochemical concepts in immobilizing, isolating or neutralizing waste derived from energy production and consumption. The book also addresses the issue of using some types of energy-derived waste as alternative raw materials. Moreover, it highlights research on how certain wastes can be used for energy production, an increasingly important aspect of modern integrated waste management strategies. The main objectives are to: (a) identify the most serious environmental problems related to various types of power generation and associated waste accumulation; (b) present strategies, based on natural analogue materials, for the immobilization of toxic and radioactive waste components through mineralogical barriers; (c) discuss modern procedures for reuse of waste or certain waste components; and (d) review the importance of geochemical modelling in describing and predicting the interaction between waste and the environment.