Leaching potential and redox transformations of arsenic and selenium in sediment microcosms with fly ash |
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| Institution: | 1. Duke University, Department of Civil & Environmental Engineering, 121 Hudson Hall, Durham, NC 27708, USA;2. RTI International, Analytical Sciences, 3040 East Cornwallis Drive, Research Triangle Park, NC 27709, USA;3. University of Kentucky, Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511, USA;4. Duke University, Division of Earth and Ocean Sciences, Nicholas School of the Environment, Durham, NC 27708, USA;1. State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China;2. School of Municipal and Environmental Engineering, Co-Innovation Center for Green Building of Shandong Province, Shandong Jianzhu University, Jinan, 250101, China;3. Faculty of Environmental Engineering, University of Kitakyushu, 1-1, Hibikino, Wakamatsu, Kitakyushu, 808-0135, Japan;4. Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), Fudan University, Shanghai, 200433, China;1. Graduate Institute of Environmental Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 106, Taiwan;1. Department of Soil and Environment, Swedish University of Agricultural Sciences, P.O. Box 7014, 750 07 Uppsala, Sweden;2. Department of Earth and Environmental Sciences, Leuven University, Kasteelpark Arenberg 20 bus 2459, 3001 Leuven, Belgium;3. Department of Food Safety and Veterinary Public Health, Istituto Superiore di Sanità, Viale Regina Elena 299, Rome 00161, Italy;4. Division of Land and Water Resources Engineering, KTH Royal Institute of Technology, Brinellvägen 28, 100 44 Stockholm, Sweden;1. Department Environment, Hygiene and Sensor Technology, Fraunhofer Institute for Building Physics IBP, Fraunhoferstraße 10, 83626, Valley, Germany;2. Chair of Urban Water Systems Engineering, School of Engineering and Design, Technical University of Munich, Am Coulombwall 3, 85748, Garching, Germany;1. Groupe Clinéa-Orpéa, clinique des addictions Montevideo, 44, rue de la Tourelle, 92100 Boulogne-Billancourt, France;2. Département de cardiologie médicale, institut de cardiologie, hôpital de la Pitié-Salpêtrière, 47, boulevard de l’Hôpital, 75651 Paris cedex 13, France |
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| Abstract: | The unintended release of coal ash to the environment is a concern due to the enrichment of contaminants such as arsenic (As) and selenium (Se) in this solid waste material. Current risk assessments of coal ash disposal focus on pH as the primary driver of leaching from coal ash. However, redox speciation of As and Se is a major factor for their mobilization potential and has received much less attention for risk assessments, particularly in disposal scenarios where coal ash will likely be exposed to microbially-driven redox gradients. The aim of this study was to demonstrate the differences of aerobic and anaerobic conditions for the leaching of As and Se from coal ash. Batch sediment-ash slurry microcosms were performed to mimic an ash spill scenario and were monitored for changes in As and Se speciation and mobilization potential. The results showed that the dissolved As concentrations were up to 50 times greater in the anaerobic microcosms relative to the aerobic microcosms during the two week incubation. This trend was consistent with As redox speciation determined by X-ray absorption spectroscopy, which indicated that 55% of the As in the solid phase at the end of the experiment was present as As(III) (a more leachable form of arsenic relative to As(V)). In the aerobic microcosms, only 13% of the As was As(III) and the rest was As(V). More than half of the Se was present as Se(IV) in the original fly ash and in the aerobic microcosms, while in the anaerobic microcosms Se was gradually transformed to less soluble Se(0) species. Likewise, dissolved Se concentrations were up to 25 times greater in the aerobic microcosms relative to anaerobic conditions. While the overall observations of As and Se mobilization potential from coal ash were consistent with expectations for aqueous and solid phase speciation of these elements, the findings directly show the relevance of these processes for coal ash disposal. These results highlight the need to select appropriate environmental parameters to include in risk assessments as well as provide potential geochemical monitoring tools through the use of dissolved Se/As ratios to determine the redox conditions of ash storage and spill sites. |
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| Keywords: | Coal combustion residuals Water quality Solid waste disposal |
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