Coal Ash Wastes: Environmental Impacts of Disposal and New Opportunities for Beneficial Reuse

Coal ash is the solid waste generated during coal combustion and includes fly ash, bottom ash, and sludge from flue gas desulfurization units. In the United States, the combustion of coal generates more than 100 million tons of coal ash each year. Half of these wastes is reused for beneficial purposes such as the manufacture of concrete and other construction materials. Coal ash is also enriched in leachable contaminants such as arsenic and selenium that can be harmful to ecosystems near coal ash disposal sites. The practice of disposing coal ash in holding ponds has recently received much attention after the catastrophic failures of ash ponds in Tennessee (2008) and in North Carolina (2014). The magnitude of these spills and the uncertain environmental costs have renewed efforts to improve policies for coal ash disposal and identify beneficial reuse opportunities.

Objectives of coal ash research in the Hsu-Kim group are two-fold: 1) We are investigating the transformations and mobilization of contaminants originating from coal ash disposal sites with the goal of improving risk assessments; and 2) We are exploring beneficial reuse opportunities for coal ash, namely the recovery of rare earth elements and other valuable metals that are enriched in coal ash. Our work has yielded insights to the geochemical properties of trace elements associated with coal ash and their potential for transformations in conditions relevant for ash disposal sites. These insights are also guiding us in our efforts to 'mine' coal ash for rare earth metals  and develop technologies for extraction and recovery.

This research is supported by the National Science Foundation and the Department of Energy.

Recent publications:

Ranking coal ash for their Se and As leaching potential, EES 2018 (open access)

TVA-Kingston Coal Ash Spill: ES&T 2009, 2010, 2013 Part 1 and Part 2

Water Quality in North Carolina lakes: ES&T 2012

Trace Element & Isotope Geochemistry: ES&T Selenium (2013), B and Sr (2014), Radioactivity (2015), Influence of redox for Se and As (Applied Geochem 2016) and for mercury (ESPI 2016)

Recovery of Rare Earth Elements: ES&T 2016 (open access), Fuel 2017, CC&GP 2017 (open access), Intl J Coal Geology (King et al. 2018) and (Taggart et al 2018), ESPI 2018.



Selected publications:

Schwartz, G.E.; Hower, J.C.; Phillips, A.L.; Rivera, N.; Vengosh, A.; Hsu-Kim H. (2018). Ranking coal ash materials for their potential to leach arsenic and selenium: The relative importance of ash chemistry and site biogeochemistry. Environmental Engineering Science.  DOI: 10.1089/ees.2017.0347 (open access)

King, J.F.; Taggart, R.K.; Smith, R.C.; Hower, J.C.; Hsu-Kim, H. (2018). Aqueous Acid and Alkaline Extraction of Rare Earth Elements from Coal Combustion Ash. International Journal of Coal Geology. 195: 75-83. DOI: 10.1016/j.coal.2018.05.009

Taggart, R.K., Hower, J.C.; Hsu-Kim H. (2018). Effects of Roasting Additives and Leaching Parameters on the Extraction of Rare Earth Elements from Coal Fly Ash. International Journal of Coal Geology. 196, 106-114. DOI: 10.1016/j.coal.2018.06.021

Schwartz, G.E.; Redfern, L.K; Ikuma, K.; Gunsch, C.K.; Ruhl, L.S.; Vengosh, A.; Hsu-Kim, H. (2016). Impacts of coal ash on methylmercury production and the methylating microbial community in anaerobic sediment slurries. Environ. Sci.: Processes & Impacts. 18, 1427-1439. DOI: 10.1039/C6EM00458J

Schwartz, G.E.; Rivera, N.A.; Lee, S.-W.; Harrington, J.M.; Hower, J.C.; Levine, K.E.; Vengosh, A.; Hsu-Kim, H. (2016). Leaching potential and redox transformations of arsenic and selenium in sediment microcosms with fly ash. Applied Geochemistry. 67, 177-185. DOI: 10.1016/j.apgeochem.2016.02.013.

Taggart, R.K.; Hower, J.C.; Dwyer, G.S.; Hsu-Kim, H. (2016). Trends in the rare earth element content of U.S.-based coal combustion fly ashes. Environ. Sci. & Technol. 50(11), 5919-5926. DOI: 10.1021/acs.est.6b00085.

Liu, Y,-T.; Chen, T.-Y.; Mackebee, W.G.; Ruhl, L.; Vengosh, A.; Hsu-Kim, H. (2013). Selenium Speciation in Coal Ash Spilled at the Tennessee Valley Authority Kingston Site. Environ. Sci. & Technol. 47(24), 14001-14009. DOI: 10.1021/es4041557.

Bartov G., Deonarine A., Johnson T.M., Ruhl L., Vengosh A., Hsu-Kim H. (2013). Environmental impacts of the Tennessee Valley Authority Kingston coal ash spill. 1. Source apportionment using mercury stable isotopes. Envir. Sci & Technol. 47(4), 2092-2099. DOI: 10.1021/es303111p.

Deonarine A., Bartov G., Johnson T.M., Ruhl L., Vengosh A., Hsu-Kim H. (2013). Environmental impacts of the Tennessee Valley Authority Kingston coal ash spill. 2. Effect of coal ash on methylmercury in historically contaminated river sediments. Envir. Sci & Technol. 47(4), 2100-2108. DOI: 10.1021/es303639d.

Ruhl L., Vengosh A., Dwyer G., Hsu-Kim H., Schwartz G., Romanski A., Smith S.D. (2012). The impact of coal combustion residue effluent on water resources: a North Carolina example. Envir. Sci & Technol. 46(21), 12226–12233. DOI: 10.1021/es303263x.