Water quality implications of the neutralization of acid mine drainage with coal fly ash from India and the United States
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Subsurface coal mining often induces the formation of acid mine drainage (AMD) in active and abandoned coal mines while coal combustion generates coal combustion residuals (CCR), including fly ash (FA), with elevated levels of toxic metals. Decades of AMD and CCR production have caused major environmental and human health impacts. Given the typically elevated level of oxides in FA, previous studies have examined its potential to neutralize AMD and remove the associated metals. While the neutralization of AMD through reaction with FA has been demonstrated to successfully remove cationic metals, the fate of oxyanion forming elements are less well studied and is the focus of this study. Here we conducted 49 different experiments in which simulated AMD solutions were interacted with representative U.S. (n = 7) and Indian (n = 6) FA samples through controlled liquid to solid ratios in short-term (24 h) and long-term (up to 5 weeks) lab-scale experiments. We show that Class-F FA, originating from Gondwana and Northeastern Tertiary coals in India, has limited neutralization capacity, while Class-C FA, with high CaO and MgO contents from Powder River coals in the U.S. has the greatest AMD neutralization capacity among the studied fly ashes. The neutralization experiments show that AMD-FA reactions cause the removal of cationic elements (i.e., Fe, Mn, and Al) from solution, while at the same time, leaching oxyanion forming elements (i.e., As, Se, Mo, Cr, B, Tl, and Sb) from the FA, increasing the potential environmental risks from the treated leachates. The magnitude of mobilization of these elements depends on their concentrations in the FA and the pH conditions. We show that using FA from the Appalachian and Illinois coals efficiently neutralizes AMD, but also results in secondary contamination of the treated effluents with oxyanion forming elements to levels exceeding drinking water and ecological standards, which could contaminate the ambient environment, whereas neuralization with Powder River Basin Class-C FA induces only limited contamination.
Published Version (Please cite this version)
Weinberg, R, R Coyte, Z Wang, D Das and A Vengosh (2022). Water quality implications of the neutralization of acid mine drainage with coal fly ash from India and the United States. Fuel, 330. pp. 125675–125675. 10.1016/j.fuel.2022.125675 Retrieved from https://hdl.handle.net/10161/26629.
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Avner Vengosh is a Distinguished Professor and Nicholas Chair of Environmental Quality at the Nicholas School of the Environment. He is the chair of the Division of Earth and Climate Sciences. Professor Vengosh and his team have studied the energy-water nexus, conducting pioneer research on the impact of hydraulic fracturing and coal ash disposal on the quantity and quality of water resources in the U.S. and China. He has also investigated the sources and mechanisms of water contamination in numerous countries across the globe, including salinity and radioactivity in the Middle East, uranium in India, fluoride in Eastern Africa, arsenic in Vietnam, and hexavalent chromium in North Carolina and China. As part of these studies, his team has developed novel geochemical and isotopic tracers that are used as fingerprints to delineate the sources of water contamination and evaluate potential risks for human health. Currently, his team is engaged in studying phosphate rocks geochemistry and the impact of fertilizers on soil and water quality, unconventional sources of critical raw materials, and potential environmental effects of lithium mining from hard rocks and brines. He is a Fellow of the Geological Society of America (GSA) and International Association of Geochemistry (IAGC). In 2019, 2020 and 2021 he was recognized as one of the Web of Science Highly Cited Researchers. He serves as an Editor of GeoHealth and on the editorial board of the journal Environmental Science and Technology. He has published 171 scientific papers in leading international journals. His recent cross-disciplinary book “Water Quality Impacts of the Energy-Water Nexus” (Cambridge University Press, 2020) provides an integrated assessment of the different scientific and policy tools around the energy-water nexus. It focuses on how water use, and wastewater and waste solids produced from fossil fuel energy production affect water quality and quantity. Summarizing cutting edge research, the book describes the scientific methods for detecting contamination sources in the context of policy and regulations.
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